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ELEMENTARY 
MECHANICAL  REFRIGERATION 

A  Simple  and  Non -Technical  Treatise 


BY 


FRED.  E.  MATTHEWS,  B.S.,M  E.?E.E. 

Member  of  American  Society  of  Mechanical  Engineers 
and  American  Society  of  Refrigerating  Engineers 


FIRST  EDITION 
SECOND  IMPRESSION 


McGRAW-HILL  BOOK  COMPANY,  INC, 
239  WEST  39TH  STREET,  NEW  YORK 

6  BOUVERIE  STREET,  LONDON,  E.  C. 


GIFT  OP 


COPYRIGHT,  1912,  BY  THE 
McGRAW-HILL  BOOK  COMPANY 


Printed  by 

The  Maple  Press 

York,  Pa. 


PREFACE 

THE  rapidly  growing  application  of  mechanical  refrigeration, 
to  new  as  well  as  to  old  industries,  has  given  rise  to  the  need  of 
a  more  general  understanding  of  its  elementary  principles.  So 
rapid  has  been  its  development,  in  fact,  that  in  the  mechanical 
world  both  laymen,  and  specialists  in  other  lines  formerly  having 
little  or  nothing  in  common  with  the  art  of  refrigeration,  have 
suddenly  awakened  to  the  fact  that  at  least  a  casual  understand- 
ing of  the  subject  has  become  almost  indispensable.  While  the 
theme  has  been  a  not  unpopular  one  among  writers  of  more  or 
less  technical  text,  yet  an  ample  opportunity  still  remains  to  help 
the  busy  man  at  the  desk,  the  drawing  board  and  the  throttle, 
to  a  better  understanding  of  the  principles  involved  and  the 
methods  employed.  If  the  following  exposition  should  be  for- 
tunate enough  to  save  the  valuable  time  of  a  busy  man  or  lighten 
the  burden  of  the  overworked  one,  its  purpose  will  not  be  unac- 
complished. 

In  its  brief  life  of  less  than  one  century  the  art  of  mechanical 
refrigeration  has  developed  from  the  scattered  and  rather  un- 
scientific application  of  a  few  more  or  less  imperfectly  understood 
natural  laws,  to  an  industry  of  almost  universal  application  and 
of  importance  second  to  none  in  the  working  out  of  the  momen- 
tous problems  of  domestic,  national,  and  international  economy. 
To  allow  the  manufacturer  to  produce  better  goods,  to  allow  the 
farmer  to  market  his  products  in  better  condition,  to  facilitate 
distribution,  to  lengthen  the  period  of  consumption  and  thereby 
eliminate  market  glut  and  famine;  to  provide  more  wholesome 
food  for  man — such  is  the  beneficent  work  of  mechanical  refrig- 
eration. 

F.  E.  MATTHEWS. 
February,  1912. 


832759 


CONTENTS. 


PAGE 
PREFACE v 

CHAPTER  I 

COLD  AND  ITS  PRODUCTION 1-10 

Refrigeration  the  Extraction  of  Heat — General  Thermal  Prop- 
erties of  Matter — The  Molecular  Theory — The  Kinetic  Theory — • 
Change  of  Condition  and  State  of  Matter  by  Heat — Heat  Units 
— Heat  Absorbing  Capacities  of  Substances — Flow  of  Heat — 
Heat  and  Cold,  Relative  Terms — Refrigeration  by  the  Melting 
of  Solids — Refrigeration  by  the  Evaporation  of  Liquids — Re- 
frigerating Temperatures  and  Pressures. 

CHAPTER  II 

THE  DEVELOPMENT  OF  MECHANICAL  REFRIGERATION 11-16 

Sources  of  Heat — Frigorific  Mixtures — Heat  Absorbing  Capac- 
ities of  Substances — Early  Experiments — Contributory  Fac- 
tors— Types  of  Small  Machines — Method  of  Operation. 

CHAPTER  III 

COMMERCIAL  SYSTEMS  OF  REFRIGERATION 17-43 

Ice  Bunker  System — Bunker  Insulation — Gravity  Brine  System — 
Elementary  Mechanical  Systems — Direct  Expansion — Brine 
Circulation  System — Ice  Freezing  Systems — Commercially 
Practical  System — Essential  Members  of  Commercial  Systems — 
Working  Mediums — The  Direct  Expansion  Compression  Sys- 
tem— Brine  Circulating  System — Congealing  Tank  System — 
Electrically  Driven  Plants — Semi-Automatic  Systems — Com- 
pletely Automatic  Systems — Thermostat  Control — Expansion 
Valve  Control — Automatic  Control  of  Feeds  in  Parallel — A  Small 
Capacity  Absorption  Machine — A  Small  Capacity  Compression 
Machine — The  Selection  of  a  Refrigerating  System. 

CHAPTER  IV 

THE  COMPRESSION  SYSTEM 44-61 

Expansion  Side — Compression  Side — Refrigeration  Available  in 
Expansion — Direct  Expansion  Cylinder  Cooling — Types  of 
Ammonia  Compressors — Vertical  Single-Acting  Compressors — 
The  Horizontal  Double-Acting  Machine — Inclosed  Crank-Case 
Compressors — The  Absorption  Refrigerating  System — Cooler — • 
Absorber — Exchanger — Analyzer — Generator — Rectifier — Con- 
denser— Cycl%  Traversed  by  Ammonia — Path  of  Cooling  Water 
— Counter-Current  Effect. 

vii 


viii  CONTENTS 

CHAPTER  V 

PAGE 

SIMPLE  COMPARISONS 62-89 

Elementary  Compression  and  Absorption  Refrigerating  Systems 
— Pump  for  Raising  Temperature — Working  Mediums — Com- 
pressor and  Expansion  Engine — Refrigeration  by  Change  of 
Temperature  of  Gases — Water  and  Ammonia  Systems — Natu- 
ral Cooling  Mediums — Heating  and  Refrigerating  Systems- 
Evaporating  and  Condensing  Members — 'Refrigerating  Furnace 
Gases  and  Cold  Storage  Air — Condensation  of  Steam  and  Am- 
monia— Refrigerating  Machine  as  a  Heat  Pump — Flow  of  Water 
and  Heat  Due  to  Difference  in  Level — Working  Pressures — • 
Evaporating  Temperatures — Evaporation  of  Water  and  Ammo- 
nia— Thermal  and  Static  Head  and  the  Flow  of  Heat  and 
Liquids — Water  Power — Pumping  Water  and  Heat — Leaks — 
Working  Limits — Multiple  Effect  Refrigerating  Machine. 

CHAPTER  VI 

ICE-MAKING  SYSTEMS 90-99 

The  Can  System — Distilling  Apparatus — High-Pressure  Sys- 
tem— Freezing  Time  Required  for  Can  Ice — The  Plate  Ice  Sys- 
tem— Inorganic  Impurities —Operation  of  Plate  System — Cen- 
tre-Freeze System — Evaporators  and  Vacuum  Distilling 
Apparatus — Combined  Can  and  Plate  Ice  Plant — Vacuum 
Distilling  System. 

CHAPTER  VII 

THE  INSTALLATION  AND  OPERATION  OF  REFRIGERATING  SYSTEMS  100-109 
Installation — Repairing  Leaks — Charging  a  Refrigerating  Sys- 
tem— Amount  of  Ammonia  Charge — Salt. 


CHAPTER  VIII 

WORKING  PRESSURES .' 110-118 

Pressure  and  Efficiency — Condenser  Pressure — Freezing  Back — 
Condition  of  Ammonia — The  Frost  Line — Insulated  Suction 
Lines. 

CHAPTER  IX 

CLEANING  THE  SYSTEM 119-125 

Defrosting  Refrigerator  Coils — Brine  Coils — Direct  Expansion 
Coils — Oil  in  the  Refrigerating  System — Oil  in  Coils — Perma- 
nent Gases — Purging — Incrustation  on  Condenser  Coils. 


CONTENTS  ix 

CHAPTER  X 

PAGE 

CAPACITY  OF  REFRIGERATING  MACHINES 126-147 

Effect  on  Secondary  Refrigerating  Mediums — Effect  on  Primary 
Refrigerating  Mediums — Effect  of  Pressure — Computed  Ca- 
pacity Example — Pounds  Refrigeration — Pounds  of  Ammonia — 
Cubic  Feet  of  Ammonia — Capacity  of  Compressor — Displace- 
ment Efficiency  of  Compressor — Apparent  Cubical  Displace- 
ment— Effect  of  Working  Pressures — B.  tu.  per  Cubic 
Foot — Cubic  Feet  Displacement  Per  Ton — Approximate  Nomi- 
nal Capacity  of  Compressors — Capacity  Determined  by  Test — 
Weighing  Primary  Refrigerant — Tonnage  Computed  from 
Quantity  of  Refrigerant — Actual  Displacement  Efficiency  of 
Compressor — Approximate  Displacement  of  Compressor — 
Apparent  Displacement — Actual  Displacement — Approximate 
Displacement  Efficiency — Computation  of  Capacity — Cooling 
Effect  Produced  on  Brine — Approximate  Cooling  Effect 
Twenty-five  Heat  Gallons  per  Ton— Actual  Cooling  Effect. 

CHAPTER  XI 

COLD-STORAGE  DUTY 148-161 

Cooling  the  Product — Water  Cooling — W6rt  Cooling — Lights — 
Cold  Losses  Through  Gold-Storage  Doors — Insulation  Losses. 

INDEX. .  163 


ELEMENTARY   MECHANICAL 
REFRIGERATION 


CHAPTER  i     ;r^j  v ,    v 

COLD  AND   ITS  PRODUCTION 
REFRIGERATION  THE  EXTRACTION  OF  HEAT 

IN  its  broader  sense  refrigeration  may  be  defined  as  the  process 
of  cooling;  or,  since  cold  is  but  the  absence  of  heat,  as  dark- 
ness is  absence  of  light,  and  dryness  is  absence  of  moisture,  in 
which  cases  the  real  entities  are  heat,  light,  and  moisture  respec- 
tively, refrigeration  may  be  more  accurately  defined  as  the 
process  of  extracting  heat.  The  study  of  refrigeration  therefore 
necessitates  the  study  of  heat. 

The  above  definition  of  Refrigeration  is  somewhat  inadequate, 
in  that  it  conveys  the  impression  that  heat  is  a  passive  element, 
while  in  reality  it  is  decidedly  an  active  one.  While  heat  may  be 
generated  by  the  performance  of  work,  as  in  the  compression  of 
gases,  or  even  when  a  piece  of  metal  is  struck  a  few  sharp  blows 
with  a  hammer  (its  appearance  being  incident  to  the  disappear- 
ance of  an  equivalent  amount  of  work),  when  once  fortified 
within  the  walls  of  matter  it  is  able  to  resist  the  most  strenuous 
efforts  to  dislodge  it  and  it  must  accordingly  be  decoyed  into 
leaving  the  substance  from  choice. 

Heat  can  best  be  coaxed  out  of  a  given  substance  by  placing 
near  it  another  substance  materially  lower  in  temperature, 
under  which  condition  its  tendency  is  to  flow  from  the  substance 
of  higher  to  that  of  lower  temperature — just  as  .water  flows  from 
a  higher  to  a  lower  level.  The  result  of  such  a  gravitation  of  heat 
is  that  the  latter  substance  is  heated  and  the  former  refrigerated. 
Wherever  there  is  a  difference  in  temperature  between  two 
bodies  there  is  always  a  tendency  for  heat  to  flow  from  that  of 
the  higher  to  that  of  the  lower  temperature,  hence  it  follows  that 
both  heating  and  refrigerating  may  take  place  at  any  point 
above  absolute  zero. 


2    ELEMENTARY  MECHANICAL  REFRIGERATION 

GENERAL  THERMAL  PROPERTIES  OF  MATTER 

Since  refrigeration  has  to  do  wholly  with  the  extraction  of 
heat,  in  order  to  arrive  at  a  clear  understanding  of  the  subject 
one  must  first  become  familiar  with  the  general  thermal  prop- 
erties of  the  substances  most  commonly  encountered  in  connec- 
tion with  refrigerating  processes,  especially  such  properties  as 
have  to  do  with  their  -capacities  for  absorbing  heat  under  different 
conditions. 

THE  MOLECULAR  THEORY 

The  molecular  theory  of  matter  assumes  that  all  the  chemical 
elements,  of  which  all  matter  is  composed,  are  made  up  of  infi- 
nitely small  particles  called  atoms.  When  elements  combine  to 
form  compounds,  such  as  when  hydrogen  combines  with  oxygen 
to  form  water,  the  atoms  of  each  element  combine  to  form  other 
infinitely  small  particles  of  matter  called  molecules.  Two  or 
more  atoms  may  combine  to  form  molecules.  Atoms  and  mole- 
cules, although  infinitely  small,  are  supposed  to  possess  all  the 
properties  of  the  respective  substances  of  which  they  are  a  part. 
The  application  of  a  sufficient  amount  of  heat  to  a  substance 
will  result  in  separating  the  molecules  into  their  constituent 
atoms ;  or  the  substances  (if  a  compound)  into  its  elemental  parts. 

Matter  may  exist  in  three  different  states,  the  solid,  the 
liquid,  and  the  gaseous,  according  to  the  amount  of  heat  that  it 
contains. 

THE  KINETIC  THEORY 

The  kinetic  theory  assumes  that  molecules  and  atoms  are  in 
constant  motion.  This  motion  is  greatly  restricted  in  solid  bodies 
because  of  the  powerful  intermolecular  attractive  forces  which 
exist  when  the  molecules  are  so  close  together.  The  motion  is 
less  restricted  in  the  liquid,  and  practically  unrestricted  in  the 
gaseous  state. 

Heat  is  a  form  of  energy.  The  application  of  heat  to  a  sub- 
stance increases  the  kinetic  energy  of  its  molecules,  enabling 
them  to  increase  their  motion  notwithstanding  the  strong  attrac- 
tive forces  exerted  to  limit  it.  The  addition  of  sufficient  heat 
to  a  solid  will  so  increase  the  energy  of  its  molecules  as  to  partially 
overcome  the  intermolecular  attractive  forces  and  allow  of  suffi- 
ciently increased  motion  to  change  the  substance  from  the  solid 
to  the  liquid  state.  A  further  application  of  heat  energy 


COLD  AND  ITS  PRODUCTION  3 

will  further  overcome  the  attractive  forces  and  change  the  sub- 
stance from  the  liquid  to  the  gaseous  state. 

In  case  of  some  complex  substances,  such  for  example  as 
ammonia  (NH8)  which  is  composed  of  the  two  elements,  nitro- 
gen (N)  and  hydrogen  (H),  a  still  further  application  of  heat 
will  effect  the  dissociation  of  its  molecules  into  atoms  of  nitrogen 
and  hydrogen. 

In  the  general  case  the  withdrawal  of  sufficient  heat  from  a 
gas  has  the  effect  of  causing  it  to  return  first  to  the  liquid,  then 
to  the  solid  state.* 

CHANGE  OF  CONDITION  AND  STATE  OF  MATTER  BY  HEAT 

Every  substance  absorbs  a  more  or  less  constant  quantity  of 
heat  for  each  degree  rise  in  temperature  in  that  substance.  This 
quantity  of  heat  expressed  in  proper  units  is  known  as  the  "specific 
heat  of  the  solid,"  the  " liquid"  or  the  "gas,"  as  the  state  of  the 
substance  in  question  may  determine. 

Each  degree  rise  in  temperature  of  a  pound  of  a  solid  substance, 
for  example,  is  attended  by  the  absorption  of  a  quantity  of  heat 
known  as  the  "specific  heat  of  the  solid."  The  absorption  of  a 
practically  fixed  quantity  of  heat  for  each  degree  rise  in  tem- 
perature will  continue  until  the  melting  point  of  the  solid  is 
reached — when  a  further  application  of  heat  will  produce  no 
further  rise  in  temperature  but  will  produce  a  change  of  state, 
liquefaction,  instead.  The  amount  of  heat  absorbed  per  pound 
during  liquefaction  is  known  as  the  "latent  heat  of  fusion"  or 
the  "latent  heat  of  the  liquid." 

When  all  of  the  substance  is  melted  a  further  application  of 
heat  will  again  produce  rise  in  temperature  and  the  amount  of 
heat  absorbed  per  pound  per  degree  rise  in  temperature  is  known 
as  the  "specific  heat  of  the  liquid." 

When  the  boiling  point  of  a  simple  substance  is  reached, t  the 
further  application  of  heat  will  not  produce  any  further  rise  in 

*  There  are  some  gases  which  cannot  be  liquefied  by  the  reduction  of  tem- 
perature alone,  high  pressure  being  also  a  requisite. 

t  In  the  case  of  complex  substances,  such,  for  example,  as  mineral  oils,  no 
absolutely  fixed  boiling  points  exist.  A  moderate  application  of  heat  to  crude 
oil  will  drive  off  one  after  another  of  the  distillates,  such  as  benzine,  gasolene, 
kerosene,  etc.,  but  while  the  temperature  at  which  each  distillate  is  driven  off 
is  different  from  that  of  the  others,  the  increase  in  temperature  as  distillation 
progresses  is  gradual  and  the  distillation  temperatures  define  the  product, 
rather  than  the  product  the  temperatures. 


4      ELEMENTARY  MECHANICAL  REFRIGERATION 

temperature,  but  a  change  of  state,  vaporization,  which  will  pro- 
gress at  a  constant  temperature  until  all  is  evaporated.  The 
quantity  of  heat  required  to  evaporate  a  pound  of  the  liquid  is 
the  " latent  heat  of  vaporization"  or  the  "latent  heat  of  the 
vapor." 

When  all  of  the  substance  is  evaporated  a  further  application 
of  heat  will  again  produce  a  rise  in  temperature  and  the  quantity 
of  heat  absorbed  per  pound  per  degree  rise  in  temperature  of  the 
vapor  is  the  " specific  heat  of  the  vapor."  Objection  might  logi- 
cally be  made  to  the  term  "  latent  heat,"  since  the  heat  disap- 
pearing when  solids  melt  and  liquids  evaporate  really  no  longer 
exists  as  heat,  but  has  been  expended  in  doing  work,  just  as  heat 
units  expended  in  a  steam  engine  are  converted  into  an  equiva- 
lent amount  of  work  measurable  in  foot-pounds.  A  common 
example  of  work  is  the  raising  of  a  weight  of  a  certain  number  of 
pounds  through  a  certain  number  of  feet  of  space  against  the 
attractive  force  of  gravity.  Heat  absorbed  in  the  process  of 
melting  and  evaporation  is  expended  in  doing  internal  work,  or 
in  overcoming  attractive  forces  between  the  molecules  of  the 
substance  melted  or  evaporated.  The  expenditure  of  heat  in 
separating  one  molecule  from  another  against  the  force  of  mole- 
cular attraction,  differs  in  no  material  sense  from  that  expended 
in  prime  movers  in  separating  heavy  weights  from  the  earth 
against  the  force  of  gravity. 

HEAT  UNITS 

The  standard  unit  generally  adopted  in  commercial  work 
among  English  speaking  people  is  the  British  thermal  unit 
(B.t.u.),  which  is  the  equivalent  of  the  amount  of  heat  required 
to  raise  the  temperature  of  one  pound  of  water  through  one 
degree  Fahrenheit  at  its  temperature  of  maximum  density,  39.1° 
Fahrenheit.  This,  it  may  be  remembered,  Joule  found  by  his 
historic  experiment  to  be  equivalent  to  772  foot-pounds  of  work. 
More  recent  experiments,  however,  have  led  to  the  adoption  of 
778  as  a  more  accurate  equivalent.  In  more  purely  scientific 
work  the  French  or  metric  unit,  the  calorie,  is  employed.  This 
unit  is  the  equivalent  of  the  amount  of  heat  required  to  raise  the 
temperature  of  one  kilogram  (2.2+pounds)  of  water  through  one 
degree  Centigrade  (1.8  degrees  Fahrenheit)  at  its  maximum  den- 
sity temperature  of  4°  Centigrade.  By  the  following  experi- 


COLD  AND  ITS  PRODUCTION  5 

tnent,  Doctor  Joule  determined  the  mechanical  equivalent  of 
heat.  A  paddle  fitted  to  a  shaft,  which  was  made  to  revolve  by 
weights  so  acting  that  the  exact  amount  of  work  done  by  them 
could  be  measured,  was  placed  in  a  cylindrical  vessel  containing  a 
definite  amount  of  water  at  a  known  temperature.  As  the  pad- 
dle revolved  the  water  was  agitated  and  the  temperature  was 
found  to  rise.  The  energy  of  the  weights  had  been  converted 
first  into  motion  of  the  paddle,  then  into  heat  in  the  water.  He 
determined  that  when  mechanical  energy  is  converted  into  heat 
the  amount  of  heat  produced  is  proportional  to  the  mechanical 
energy  expended,  and  specifically,  that  one  calorie  represents  424 
kilogrammeters  of  energy.  The  mechanical  equivalent  of  heat 
or  as  it  is  called  Joule's  equivalent,  is  424  kilogrammeters. 
In  the  English  system  the  same  equivalent  is  772.55  foot-pounds, 
or  one  B.t.u.,  later  definitely  fixed  as  778  foot-pounds. 

Since  the  amount  of  heat  required  to  raise  the  temperature  of 
one  pound  of  water  one  degree  Fahrenheit  has  been  made  the 
standard  unit  by  which  other  quantities  of  heat  are  measured, 
the  latent  and  specific  heats  above  defined  are  expressed  in  B.t.u. 
The  specific  heat  of  water  is  unity. 

Since  the  amount  of  heat  required  to  raise  the  temperature  of 
one  pound  of  ice  one  degree  is  one-half  that  of  water,  the  specific 
heat  of  water  in  the  solid  state  is  one-half  B.t.u.,  or  simply  0.5. 
Similarly,  the  latent  heat  of  fusion  of  water  is  144*,  the  latent 
heat  of  vaporization  is  966,  and  the  specific  heat  of  steam,  accord- 
ing to  whether  it  is  taken  at  constant  pressure  or  constant  volume, 
is  0.480  and  0.346,  respectively. 

It  will  be  noted  that  the  specific  heat  at  constant  pressure  is 
somewhat  greater  than  the  specific  heat  at  constant  volume.  In 
determining  the  latter,  the  gas  is  not  allowed  to  expand;  in  other 
words,  it  is  maintained  at  a  "  constant  volume."  In  determining 
the  former,  the  volume  is  allowed  to  increase  with  the  addition  of 
heat  just  sufficiently  to  maintain  a  "  constant  pressure."  The 

*  At  the  New  York  meeting  of  the  American  Society  of  Mechanical  Engi- 
neers, a  committee  appointed  by  that  society  to  suggest  a  standard  tonnage 
basis  for  refrigeration  proposed  as  a  unit  for  measuring  cooling  effect,  the 
equivalent  of  the  heat  required  to  melt  one  pound  of  ice,  i.e.,  144  B.t.u.  The 
unit  for  a  ton  of  2000  pounds  of  ice-melting  capacity  was  then  fixed  at  288,000 
B.t.u.,  which,  since  the  rating  is  always  expressed  in  tons  per  24  hours,  makes 
a  ton  duty  equivalent  to  the  rate  of  12,000  B.t.u.  per  hour,  or  200  B.t.u.  per 
minute. 


6     ELEMENTARY  MECHANICAL  REFRIGERATION 

work  done  by  the  gas  in  expanding  is  equivalent  to  the  excess  of 
the  amount  of  heat  supplied  in  the  case  of  constant  pressure, 
over  that  required  to  produce  the  same  rise  in  temperature  at 
constant  volume. 

HEAT  ABSORBING  CAPACITIES  OF  SUBSTANCES 

Under  a  given  pressure  there  are  for  every  substance,  definite 
and  fixed  temperatures  at  which  that  substance  will  change  from 
one  of  its  three  states,  the  solid,  the  liquid,  or  the  gaseous,  to 
another;  and  at  each  change  that  substance  absorbs  or  liberates 
an  amount  of  heat,  which,  though  varying  slightly  at  different 
temperatures,  is  more  or  less  a  constant  and  characteristic  of  that 
particular  change  of  state  of  that  particular  substance.  So  con- 
stant is  the  temperature  at  which  these  changes  of  state  take 
place  that  the  simple  determination  of  the  boiling  point  under 
atmospheric  pressure,  of  some  of  the  more  common  liquids  such 
as  alcohol,  water,  ammonia,  etc.,  is  sufficient  to  establish  their 
identities.  At  atmospheric  pressure  alcohol  boils  at  173°  Fahren- 
heit, water  at  212°  Fahrenheit  and  ammonia  at  —  283/2°  Fahren- 
heit. Except  for  the  question  of  the  facility  of  conducting  the 
experiments,  the  freezing  points  of  the  liquids  in  question  might 
just  as  well  be  employed  to  determine  their  identity.  Abso- 
lute alcohol,  for  example,  freezes  at  —  202°  Fahrenheit  and  water 
at  32°  Fahrenheit.  In  general,  the  addition  of  a  foreign  sub- 
stance capable  of  being  dissolved  in  either  of  these  liquids  has 
the  effect  of  lowering  the  freezing  point  and  raising  the  boiling 
point. 

Similarly,  the  amount  of  heat  absorbed  or  liberated  when  a 
fixed  quantity  of  one  of  the  above  liquids  changes  state  is  so 
nearly  a  constant  that  it  could  be  employed  to  establish  the 
identity  of  the  liquid  were  it  not  for  the  difficulty  of  determining 
the  exact  amount  of  heat  involved.  A  pound  of  water,  for  ex- 
ample, absorbs  144  B.t.u.  in  changing  from  the  solid  to  the  liquid 
state,  and  966  B.t.u.  in  changing  from  the  liquid  to  the  gaseous 
state.  Similarly,  in  changing  from  the  liquid  to  the  gaseous  state 
a  pound  of  anhydrous  ammonia  absorbs  555  B.t.u. 

FLOW  OF  HEAT 

It  has  been  stated  above  that  there  is  always  a  tendency  for 
heat  to  flow  from  one  body  to  another  wherever  there  is  a  differ- 
ence in  temperature.  For  the  present  purpose,  it  may  be  gen- 


COLD  AND  ITS  PRODUCTION  7 

erally  stated  that  the  rate  at  which  the  passage  of  heat  takes 
place  is  directly  proportional  to  the  difference  in  temperature, 
and  inversely  proportional  to  the  amount  of  resistance  offered  to 
its  passage  by  interposed  substances.  The  flow  of  heat  through 
substances  all  of  which  are  to  a  greater  or  less  degree  conductors 
of  heat,  is  analogous  to  the  flow  of  electricity  in  an  electrical  con- 
ductor, which,  as  expressed  in  Ohm's  law,  is  directly  proportional 
to  the  voltage  or  " electromotive  force"  and  inversely  propor- 
tional to  the  electrical  resistance  of  the  conductor.  Expressed 
as  an  equation 

E  (Electro  Motive  Force  in  Volts.) 

C=— ,  or  (current  in  amperes)  = /T>     .  , : — ^r c 

B/  (Resistance  in  Ohms) 

The  flow  of  heat  may  also  be  compared  to  that  of  a  gas  or  a 
liquid  in  a  pipe  where  the  quantity  discharged  is  directly  pro- 
portional to  the  difference  in  pressure  and  inversely  proportional 
to  the  friction  encountered. 

Passage  of  heat  may  take  place  by  convection,  conduction,  or 
radiation,  and  in  the  general  case,  by  all  three  methods  simul- 
taneously, so  that  the  mathematical  expression  for  the  total  heat 
transfer  between  two  bodies  of  different  temperatures  becomes 
somewhat  complex.  Fortunately,  in  a  great  number  of  engineer- 
ing problems  the  amount  of  heat  transmitted  by  conduction  is  so 
far  in  excess  of  that  transmitted  by  radiation  and  convection  that 
the  last  two  factors  may  be  ignored  entirely  or  introduced  in 
terms  of  conduction. 

HEAT  AND  COLD,  RELATIVE  TERMS 

Much  of  the  popular  misconception  of  the  art  of  refrigeration 
has  arisen  through  our  proneness  to  group  temperatures  into  such 
technically  meaningless  classes  as  "warm,"  "hot,"  "cool"  and 
"cold,"  according  to  their  apparent  relation  to  the  widely  varying 
temperatures  of  our  -surroundings,  which  we  erroneously  come  to 
look  upon  as  a  kind  of  variable  zero  from  which  all  other  tem- 
peratures should  be  measured.  This  in  turn  gives  rise  to  the 
erroneous  notion  that  a  substance  is  capable  of  heating  or  refrig- 
erating other  substances  according  to  whether  it  appears  hot  or 
cold  to  the  touch. 

While  this  gives  a  more  or  less  correct  idea  as  to  the  ability 
of  the  substance  in  question  to  heat  or  refrigerate  our  bodies,  it 


8      ELEMENTARY  MECHANICAL  REFRIGERATION 

cannot  in  the  general  case  give  any  idea  of  its  ability  to  heat  or 
refrigerate  other  bodies  at  widely  different  temperatures. 

If  one  places  his  hand  in  water  much  higher  in  temperature 
than  his  body  it  is  said  to  be  hot.  If  he  places  his  other  hand  in 
water  much  lower  in  temperature  than  his  body,  it  is  said  to  be 
cold.  If  both  hands  are  then  placed  in  water  of  the  same  temper- 
ature as  his  body  it  will  feel  hot  to  the  hand  that  was  in  the  cold, 
and  cold  to  the  hand  that  was  in  the  hot  water. 

Since  heat  and  cold  are  relative  terms  arising  from  comparison 
with  normal  temperatures,  a  temperature  described  as  being  hot 
in  winter  might  be  regarded  as  being  cold  in  summer.  The  fact 
that  an  object  is  already  cold  does  not  prevent  its  being  made 
still  colder  by  the  further  removal  of  heat.  The  coldest  substances 
known  are  still  possessed  of  a  large  quantity  of  heat,  only  part  of 
which  can  be  abstracted  by  any  known  method.  Could  all  of 
the  heat  be  removed  from  a  substance,  the  resulting  temperature 
would  be  absolute  zero,  or  about  466°  below  our  present  Fahren- 
heit zero.  At  this  point  all  chemical  action  would  cease,  and 
neither  animal  nor  vegetable  life  could  exist. 

Since  refrigeration,  which  occurs  whenever  there  is  a  flow  of 
heat  from  a  relatively  warmer  to  a  relatively  cooler  body,  may 
take  place  at  any  temperature  regardless  of  whether  it  is  above 
or  below  that  of  our  surroundings,  the  melting  of  iron  in  a  blast 
furnace  may  be  said  to  refrigerate  its  contents  just  as  truly  as 
the  melting  of  ice  does  the  contents  of  a  refrigerator. 

Where  the  refrigerating  effect  is  due  to  the  direct  passage  of 
heat  from  one  substance  to  another,  it  is  almost  axiomatic  that 
the  cooling  of  one  can  take  place  only  with  the  equivalent  heating 
of  the  other.  The  heating  and  cooling  are  the  same  operation 
seen  from  two  diametrically  opposite  viewpoints. 

REFRIGERATION  BY  THE  MELTING  OF  SOLIDS 

The  most  common  examples  furnished  by  nature,  of  processes 
by  which  the  refrigerating  of  one  body  is  accomplished  by  a  cor- 
responding heating  of  another,  are  the  changing  of  water  into 
ice  and  its  subsequent  melting  to  form  water.  In  the  former 
process,  heat  passes  from  the  water  to  the  air,  the  water  being 
refrigerated  and  the  air  heated.  Conversely  in  the  latter  process, 
heat  passes  from  the  air  to  the  ice,  the  air  being  refrigerated  and 
the  water  heated.  Both  these  processes  ordinarily  take  place 
under  atmospheric  pressure  and  at  32°  Fahrenheit. 


COLD  AND  ITS  PRODUCTION  9 

As  another  example  may  be  cited  the  congealing  and  subse- 
quent melting  of  mercury  at  —39°  Fahrenheit,  and  that  of  cast 
iron  at  about  2000°  Fahrenheit,  or  in  fact  that  of  any  fusible 
substance  at  its  temperature  of  fusion.  In  the  foregoing  exam- 
ples, absorption  of  heat,  or  refrigeration,  involves  the  latent  heat 
of  fusion  of  the  substances,  water,  mercury  and  iron,  in  question. 

REFRIGERATION  BY  THE  EVAPORATION  OF  LIQUIDS 
Another  means  of  bringing  about  the  absorption  of  heat  or 
refrigeration  is  by  the  evaporation  of  liquids.  This  involves  the 
latent  heat  of  vaporization,  and  the  fact  that  the  latent  heat  of 
vaporization  of  a  substance  is  greater  than  the  latent  heat  of 
fusion  is  one  reason  why  methods  involving  the  former  factor 
are  the  more  commonly  employed  in  connection  with  artificial 
refrigerating  systems. 

Probably  the  most  common  example  in  nature  of  refrigera- 
tion produced  by  the  evaporation  of  a  liquid,  is  the  cooling 
effect  of  summer  showers,  in  which  the  evaporation  of  a  part 
of  the  water  precipitated  cools  the  dry,  hot  air  which  absorbs 
it.  Another  well-known  cooling  effect  is  encountered  when  one 
sits  in  a  draft  after  perspiring  freely.  The  effect  of  the  draft  is 
to  continually  displace  the  stratum  of  warm,  saturated  air  lying 
next  the  skin  by  cool,  dry  air.  To  evaporate  the  moisture,  heat 
is  abstracted  both  from  the  air  and  from  the  skin.  This  con- 
tinued rapid  abstraction  of  heat  from  the  skin  is  more  rapid  than 
the  heat  supply  from  the  blood.  The  temperature  of  the  skin 
falls  so  rapidly  as  to  eventually  result  in  congestion  and  the 
resultant  effect  known  as  a  cold.  Among  less  common 
examples  may  be  cited  the  method  of  cooling  drinking  water 
sometimes  employed  on  shipboard,  i.e.,  by  exposing  it  to  the 
wind  in  porous  tile  vessels,  the  evaporation  of  a  part  of  the 
water  through  the  walls  of  which  refrigerates  the  portion 
remaining  in  the  vessel.  In  India  water  is  actually  frozen  by  the 
rapid  evaporation  of  part  of  it  exposed  in  shallow  earthen  trays 
to  the  clear,  dry  night  air. 

REFRIGERATING  TEMPERATURES  AND  PRESSURES 

Evaporation  can  only  take  place  when  a  fixed  quantity  of 
heat  is  absorbed.  Conversely,  absorption  of  heat,  or  refrigera- 
tion, always  occurs  when  a  substance  is  evaporated,  whether  the 
evaporation  takes  place  rapidly  at  the  boiling  point  or  slowly  at 


10    ELEMENTARY  MECHANICAL  REFRIGERATION 

a  temperature  far  below  its  boiling  point.  Since  no  two  simple 
substances  boil  under  the  same  conditions  of  temperature,  it 
follows  that  it  may  be  possible  to  produce  refrigeration  either  at 
a  given  temperature  by  the  evaporation  of  different  substances 
at  different  pressures,  or  within  certain  limits,  to  produce  refrig- 
eration at  quite  widely  different  temperatures  by  the  evaporation 
of  the  same  substance  at  different  pressures. 

In  general  the  most  desirable  working  medium  is  that  sub- 
stance which  has  either  its  latent  heat  of  vaporization  or  latent 
heat  of  fusion  available  under  not  too  abnormal  conditions  of 
temperature  and  pressure. 

While  evaporation  of  water  in  the  tubes  of  a  water-tube  boiler 
refrigerates  the  furnace  gases  in  almost  the  same  way  as  the 
evaporation  of  other  liquids  (so-called  refrigerating  media)  does 
the  air  surrounding  the  similar  pipe  coils  in  direct-expansion 
refrigerating  systems,  the  fact  that  the  latent  heat  of  vaporiza- 
tion of  steam  is  not  generally  available  at  less  than  212°  Fahren- 
heit under  atmospheric  pressure  has  up  to  the  present  time 
prevented  the  extensive  use  of  that  medium  in  connection  with 
what  are  commonly  termed  "refrigerating  systems." 

The  availability  of  the  latent  heat  of  vaporization  of  water 
at  32°  Fahrenheit  requires  the  usually  prohibitive  vacuum  of 
29.76  inches  of  mercury,  but  the  fact  that  the  latent  heat  of 
fusion  of  water  is  available  at  32°  Fahrenheit  under  atmospheric 
pressure,  allows  artificial  ice  to  become  as  important  a  factor  in 
our  general  scheme  of  domestic  and  commercial  economy  as  nat- 
ural ice,  the  freezing  and  subsequent  melting  of  which  in  our 
lakes  and  rivers  protects  both  animal  and  vegetable  life  through 
the  tempering  of  extreme  temperatures,  is  in  Nature's  economy. 


CHAPTER  II 

THE   DEVELOPMENT   OF   MECHANICAL 
REFRIGERATION 

SOURCES  OF  HEAT 

IT  has  already  been  stated  that  in  the  study  of  mechanical 
refrigeration  the  real  entity  to  which  we  must  direct  our  atten- 
tion is  heat.  The  two  principal  sources  of  heat  are  chemical 
reaction  and  solar  radiation.  The  most  important  of  all  chem- 
ical reactions  to  the  engineer,  and  in  fact  to  the  mechanical  world, 
is  that  of  combustion;  but  even  the  heat  due  to  combustion  has 
its  origin  largely  in  solar  radiation. 

Primitive  man  had  to  depend  largely  upon  solar  radiation  for 
his  physical  comfort.  When  he  enjoyed  warm  weather,  however, 
his  food  would  not  keep,  and  when  the  weather  was  cold  enough 
to  keep  his  food  he  had  to  resort  to  the  combustion  of  the  more 
easily  procurable  fuels  in  order  to  keep  warm. 

Long  before  the  appearance  of  man,  however,  radiant  solar 
energy  had  been  carrying  out  a  process  by  which  carbon  dioxide 
from  the  air  was  broken  up  into  free  oxygen  and  fixed  carbon 
in  the  plant  structure  of  vast  vegetable  growths,  which  after 
becoming  buried  under  the  surface  of  the  earth  and  falling  into 
partial  decay,  formed  our  present  coal  deposits.  Radiant  solar 
energy  available  through  chemical  reaction,  the  combustion  of 
coal,  now  supplies  the  greater  part  of  the  power  required  to  move 
our  commercial  world. 

While  man's  industry  in  digging  in  the  ground  for  stored  heat 
enabled  him  to  solve  the  problem  of  keeping  warm,  it  remained 
for  his  ingenuity  to  devise  methods  for  preserving  his  food — first 
by  the  direct  use  of  the  natural  cooling  medium,  ice,  and  later, 
as  his  creative  ability  increased  by  the  indirect  use  of  artificial 
cold  produced  by  the  expenditure  of  the  natural  heating  material, 
coal. 

Man's  first  lesson  in  refrigeration  taught  him  that  water 
solidified  by  some  mysterious  property  possessed  by  the  cold 
north  wind  could  be  preserved  to  serve  him  during  the  summer,  if 


12    ELEMENTARY  MECHANICAL  REFRIGERATION 

carefully  stored  away  in  caves  in  the  earth.  With  certain  minor 
refinements  in  the  operations,  this  same  crude  method  employed 
by  our  primeval  ancestors  is  still  being  used  to  no  inconsiderable 
extent  to-day.  The  fact,  however,  that  summer  requirements 
must  be  anticipated  at  least  one  season  by  both  Nature  and  man, 
has  combined  with  a  score  of  other  elements  to  force  the  intro- 
duction of  more  scientific  methods. 

FRIGORIFIC  MIXTURES 

Laboratory  methods  of  producing  low  temperature  by  means 
of  so-called  "frigorific  mixtures,"  by  which  a  perceptible  drop  in 
temperature  is  produced  by  certain  endothermic  chemical  reac- 
tions and  solutions  have  been  known  for  at  least  three  centuries. 

Probably  the  most  common  example  of  a  frigorific  mixture  is 
that  of  ice  or  snow  and  salt.  The  addition  of  a  foreign  substance 
to  a  liquid  lowers  its  freezing  point.  The  effect  of  the  addition  of 
different  amounts  of  common  salt  (NaCl)  and  that  of  calcium 
chloride  (CaCl)  is  clearly  set  forth  in  the  table  on  page  145.  Since 
the  addition  of  10  per  cent,  of  salt,  by  weight,  to  water  lowers  its 
freezing  point  to  18.7°  Fahrenheit  and  prevents  its  changing  to 
the  solid  state  till  that  temperature  is  reached,  it  would  follow 
that  the  addition  of  the  same  percentage  of  salt  to  snow  or  finely 
divided  ice  would  cause  it  to  return  to  the  liquid  state  at  all 
temperatures  above  18.7°  Fahrenheit.  The  result  is  that  the 
ice  at  once  begins  to  melt,  but  to  do  so  it  must  absorb 
144  B.t.u.  of  heat  per  pound,  and  in  the  event  that  this  heat  is 
not  forthcoming,  the  temperature  of  the  mixture  will  continue  to 
fall  until  the  freezing  point  corresponding  to  the  per  cent,  solu- 
tion is  reached.  At  this  point  it  will  continue  to  exist  in  the 
solid  state,  and  aside  from  the  lesser  intimacy  of  the  mixture  of 
the  two  constituents,  ice  and  salt,  will  be  the  same  substance  as 
frozen  brine  of  the  same  per  cent,  composition,  and  will  exist 
under  the  same  conditions  of  temperature. 

HEAT  ABSORBING  CAPACITIES  OF  SUBSTANCES 

The  heat  absorbing  capacity  of  a  substance  when  only  its 
temperature  is  raised,  and  its  state  remains  the  same,  is  com- 
paratively small.  That  of  water  is  1  B.t.u.  per  degree  rise  in 
temperature,  in  the  liquid  state,  and  less  in  both  the  solid  and 
gaseous  states.  The  specific  heat  of  other  substances  in  all  three 
states  is  in  the  general  case  less  than  unity  or  that  of  water  in 
the  liquid  state. 


DEVELOPMENT  OF  MECHANICAL  REFRIGERA  TION  13 

The  heat  absorbing  capacity  of  a  substance  available  in  its 
change  of  state,  involving  its  latent  heat  of  fusion  and  vaporiza- 
tion, is  comparatively  large.  That  of  water  is  144  B.t.u.  for  fu- 
sion, and  about  966  B.t.u.  for  evaporation. 

In  general,  the  greatest  heat  absorbing  capacity  of  any  sub- 
stance is  in  its  latent  heat  of  vaporization  available  at  its  boiling 
point. 

Since  increasing  the  pressure  has  the  effect  of  raising  the  boiling 
point,  or  the  temperature  at  which  the  liquid  vaporizes,  and  de- 
creasing the  pressure  has  the  effect  of  lowering  it,  it  is  only  nat- 
ural that  reduction  in  pressure  below  that  of  the  atmosphere  (or 
vacuum)  was  first  employed  in  attempts  to  cause  some  of  the 
better  known  liquids  to  boil  at  sufficiently  low  temperatures  to 
produce  artificial  "cold." 

EARLY  EXPERIMENTERS 

While  there  is  evidence  that  some  little  experimenting  was 
done  with  liquids  under  vacuum  as  early  as  1755  there  is  no 
authentic  information  that  anything  of  real  importance  was 
accomplished  until  the  early  part  of  the  last  century,  when  sev- 
eral independent  inventors  built  experimental  machines,  none  of 
which,  however,  seem  to  have  produced  any  very  encouraging 
results  until  Jacob  Perkins,  an  Englishman,  developed  an  ether- 
compression  machine  which  he  patented  in  1834. 

Perkins  operated  his  ether-compression  machine  under  vacuum, 
much  as  our  present-day  ammonia-compression  machines  are 
operated  when  low  temperatures  are  required.  His  patent  of 
August,  1834,  describes  his  machine  as  being  composed  of  the 
four  principal  parts  which  constitute  our  present  machines,  viz., 
a  containing  chamber  or  evaporator  in  which  the  refrigerating 
medium  evaporates,  and  through  the  walls  of  which  it  absorbs  heat 
from  the  substance  it  is  desired  to  refrigerate;  a  pump  or  com- 
pressor for  drawing  the  evaporated  refrigerant  from  its  contain- 
ing chamber  'and  exerting  upon  it  sufficient  pressure  to  cause  it 
to  liquefy  when  cooled;  the  cooler  or  condenser  consisting  of  a 
coil  of  pipes  submerged  in  water,  and  in  which  the  refrigerant  is 
cooled  and  liquefied  after  compression,  and  a  regulating  or  ex- 
pansion valve  for  controlling  the  flow  of  the  refrigerant  liquefied 
in  the  condenser  as  it  passes  under  the  higher  condensing  pres- 
sure to  the  evaporator  maintained  under  a  lower  pressure  due  to 
the  action  of  the  compressor. 


14    ELEMENTARY  MECHANICAL  REFRIGERATION 

The  evaporator  shown  in  the  Perkins  patent  consists  of  a 
circular  tank  made  of  two  dished  metallic  disks,  which  receptacle 
was  submerged  in  the  fluid  to  be  refrigerated.  The  compressor 
was  designed  to  be  operated  by  hand,  but  otherwise  the  general 
arrangement  of  its  working  parts,  except  for  the  fact  that  the 
cylinder  was  inverted,  was  very  much  the  same  as  that  of  our 
present  small  single-acting  ammonia  compressors  with  both  suction 
and  discharge  valves  in  the  head.  A  simple  submerged  condenser, 
consisting  of  a  single  zigzag  coil,  and  a  hand-operated  expansion 
valve  were  employed. 

Both  the  compression  and  the  absorption  machines  find  their 
origin  in  the  demonstrated  possibility  of  liquefying  so-called 
gases.  In  1823  Faraday  announced  to  the  world  that  he  had 
succeeded  in  liquefying  chlorine,  ammonia  and  carbon-dioxide,  as 
well  as  several  other  gases  of  less  importance  to  the  refrigerating 
industry. 

By  the  same  method  by  which  Faraday  first  accidentally  lique- 
fied chlorine,  carbon-dioxide,  ammonia,  sulphur-dioxide,  methyl- 
ether,  Pictet  fluid,  sulphuric  ether,  ethyl  chloride,  water,  and  other 
substances  may  be  liquefied  experimentally  under  the  proper  con- 
ditions of  temperature  and  pressure. 

The  first  ammonia-absorption  machine  recognized  as  such  was 
invented  by  Carre  about  the  year  1855,  in  which  same  year  Harri- 
son, an  Australian,  and  Professor  Twining,  an  American,  are  said 
to  have  independently  perfected  the  Perkins  ether  machine,  the 
latter  inventor  having  performed  the  then  marvelous  feat  of  arti- 
ficially freezing  blocks  of  ice  with  fish  inside. 

CONTRIBUTORY  FACTORS 

Not  the  least  among  the  influences  that  have  combined  to 
forward  the  development  of  mechanical  refrigeration  has  been  the 
pollution  by  sewage  of  the  water  from  which  the  natural  ice  crops 
are  harvested.  This  has  been  especially  true  since  it  has  been 
demonstrated  that  negative  bacteriological  tests,  no  matter  how 
carefully  conducted,  are  not  insurance  against  typhoid,  and  there 
is  accordingly  well-founded  and  rapidly  growing  prejudice  against 
all  ice  known  to  be  cut  from  sewage-bearing  streams  and  lakes. 

The  breweries  were  among  the  first  to  adopt  improved  methods 
of  cooling,  largely  because  of  contamination  of  products  through 
the  unsanitary  conditions  inevitably  resulting  from  the  use  of  ice. 


DEVELOPMENT  OF  MECHANICAL  REFRIGERATION  15 

This,  together  with  the  heavy  labor  charge  which  it  entails,  forced 
the  development  of  a  system  of  mechanical  refrigeration.  While 
the  item  of  contamination  was  somewhat  less  important  in  the 
abattoirs  than  in  the  breweries,  the  enormous  amounts  of  ice  con- 
sumed and  the  uncertainty  of  the  natural  crop,  made  the  adoption 
of  mechanical  refrigeration  in  this  industry  imperative  from  an 
economic  standpoint. 

In  cold-storage  work  the  inability  of  ice,  without  the  addition 
of  salt,  to  produce  sufficiently  low  temperatures  to  satisfactorily 
preserve  many  perishable  products,  has  of  late  years,  at  least, 
probably  been  the  most  potent  factor  in  the  combination  to  force 
the  substitution  of  mechanical  systems  for  ice  in  the  cold-storage 
industry. 

The  demand  for  artificial  means  for  producing  refrigeration 
having  first  appeared  among  the  larger  industries  above  cited,  the 
builders  of  refrigerating  machines  first  set  about  to  supply  systems 
best  adapted  to  their  peculiar  requirements.  Later  as  the  require- 
ments of  the  larger  consumers  of  cold  began  to  show  signs  of  having 
limitations,  the  builders  began  to  look  for  other  fields  and  quite 
naturally  began  to  develop  systems  better  adapted  to  the  require- 
ments of  smaller  consumers  of  ice.  While  the  idea  is  still  current 
with  a  certain  class  of  consumers  that  food  products  kept  in 
mechanically  cooled  compartments  suffer  thereby,  the  intelligent 
merchant  is  willing  to  acknowledge  the  superiority  of  mechanical 
cooling  means  in  almost  every  case. 

TYPES  OF  SMALL  MACHINES 

The  chief  factor  which  fixes  the  capacity  limit  under  which  it 
becomes  commercially  impracticable  to  install  small  mechanical 
refrigerating  plants  has  been  the  cost  of  attendance  which  is  practi- 
cally as  great  for  all  smaller  sizes  as  for  those  of  from  five  to  ten 
tons  capacity,  and  this,  in  the  general  case  in  which  steam  power 
is  employed  24  hours  per  day,  solely  for  the  operation  of  the  re- 
frigeration plant,  becomes  practically  prohibitive.  The  first  step 
toward  surmounting  this  obstacle  was  to  operate  the  plant  in  the 
daytime  only  in  order  to  eliminate  the  expense  of  night  attendance. 
In  order  to  do  this  the  brine-circulating  system  commonly  called 
the  "  brine  system,"  which  will  be  described  in  detail  later,  was 
'introduced.  The  brine  system,  however,  usually  consumes  power 
24  hours  per  day,  and  in  order  to  reduce  this  expense  the  "con- 


16    ELEMENTARY  MECHANICAL  REFRIGERATION 

gealing-tank "  system,  which  will  also  be  described  in  detail  later, 
is  employed  to  some  considerable  extent. 

METHOD  OF  OPERATION 

Where  steam  is  not  required  for  other  purposes  and  the  amount 
of  power  necessary  for  the  refrigerating  plant  is  small,  the  substi- 
tution of  combustion-engine  power  is  often  capable  of  reducing  the 
cost  of  fuel  as  well  as  that  of  attendance;  the  former  where  cheap 
kerosene,  crude  or  fuel  oils  of  light  density  can  be  procured,  and 
the  latter  where  licensed  attendants,  insurance,  and  other  factors 
work  disadvantageously  for  the  small  steam  plant. 

The  comparatively  low  cost  of  power  produced  by  combustion 
engines,  coupled  with  the  slight  expense  for  attendance  now 
made  possible  by  the  application  of  certain  automatic  regulating 
and  safety  devices,  makes  this  type  of  plant,  when  properly  in- 
stalled either  with  or  without  "congealing  tanks"  as  the  case  may 
require,  a  most  practical  and  satisfactory  plant  for  the  small  con- 
sumers of  ice.  To  the  end  of  producing  a  small  mechanical  refrig- 
erating plant  capable  of  operating  with  still  less  attendance,  so- 
called  completely  automatic  systems  which  will  also  be  described 
in  detail,  have  been  developed.  While  it  is  a  fallacy  to  suppose 
that  these  machines  will  operate  without  some  attendance,  they 
are  often  capable  of  operation  with  far  less  attendance  than  any 
other  type,  and  were  it  not  for  the  usually  comparatively  high 
cost  of  electric  power  necessary  for  the  operation  of  a  completely 
automatic  plant,  the  advantages  gained  would  undoubtedly  more 
than  compensate  for  the  high  first  cost  of  such  plants. 

No  one  type  of  plant  can  be  expected  to  be  the  most  advanta- 
geous under  all  requirements,  and  the  relative  advantages  and 
disadvantages  of  one  over  the  other  in  first  cost,  operating  cost, 
superiority  of  design,  and  safety  should  be  carefully  considered 
and  balanced  up  before  a  selection  is  made. 


CHAPTER  III 
COMMERCIAL  SYSTEMS  OF  REFRIGERATION 

ABSORPTION  AND  COMPRESSION  SYSTEM 

PRACTICAL  mechanical  refrigeration  may  be  said  to  date  back  to 
1855,  in  which  year  the  ammonia-absorption  machine  was  invented 
by  Carre,  and  the  Perkins  ether-compression  machine,  patented  in 
1834,  was  simultaneously  commercialized  by  two  different  in- 
ventors in  two  different  countries.  It  is  a  rather  strange  coinci- 
dence that  the  development  of  the  two  systems  so  commonly 
employed  to-day, i.e., the  absorption  and  the  compression  systems, 
should  have  been  commenced  the  same  year. 

Generally  speaking,  while  both  the  absorption  and  the  com- 
pression systems  have  been  employed  in  connection  with  both  the 
direct  expansion  and  the  brine  systems  for  the  production  of  both 
medium  and  extremely  low  temperatures,  brine  has  been  used  more 
commonly  in  connection  with  the  absorption  machine  and  direct 
expansion  in  connect  ion  with  the  compression  machine.  The  former 
has  been  employed  more  frequently  for  extremely  low  and  the  latter 
for  comparatively  low  temperatures.  The  absorption  machine 
is  generally  conceded  to  be  more  economical  than  the  compres- 
sion machine  when  producing  extremely  low  temperatures,  under 
which  condition,  because  of  the  lightness  of  the  gas  under  the 
correspondingly  low  pressures,  the  compression  machine  loses 
greatly  in  both  efficiency  and  capacity.  At  the  present  time,  how- 
ever, it  is  problematical  whether  the  substitution  of  the  higher- 
efficiency  gas  engine  as  a  prime  mover  for  the  inherently  low- 
efficiency  steam  engine  will  not  put  the  compression  system  in 
position  to  produce  as  economical  results  as  the  absorption  sys- 
tem, even  under  the  disadvantage  of  low  temperatures. 

Since  the  compression  system  is  in  far  more  common  use  today, 
and  since  a  large  number  of  the  parts  of  the  two  systems  are  com- 
mon (see  Fig.  22),  the  details  of  construction  of  the  compression 
machine  will  first  be  considered. 

The  function  of  a  refrigerating  means,  whether  it  be  an  ab- 
sorption or  a  compression  machine,  or  simply  a  bunker  full  of  ice, 
is  to  provide  a  heat-absorbing  medium  which,  after  it  has  absorbed 


18    ELEMENTARY  MECHANICAL  REFRIGERATION 


its  fill  of  heat  from  the  products  to  be  cooled  in  the  cold-storage 
rooms,  may  be  removed  from  the  coolers  so  that  the  heat  absorbed 
may  also  be  removed.  After  its  removal  from  the  coolers,  this 
medium  may  be  divested  of  its  heat,  after  which  it  may  be  allowed 
to  return  to  the  coolers  to  absorb  more  heat,  as  in  the  case  of 
ammonia  or  brine  circulated  through  coolers;  or  it  may  be  thrown 
away  and  a  new  supply  introduced,  as  in  the  case  of  cooling  by 
ice. 

ICE  BUNKER  SYSTEM 

Bunkers  for  ice,  or  other  cooling  means,  are  usually  constructed 
in  the  form  of  a  tank  with  one  side  removed,  as  shown  in  Fig.  1, 

Insulated  Refrigerator  amPleS  PaC6S  f°r    ducts  be- 

ing   allowed    between    the 

sides  of  the  tank  and  the 
sides  of  the  room  to  permit 
the  air  to  circulate  freely. 
The  ice  in  this  case  is  stored 
on  a  water-tight  floor  over 
the  compartment  to  be 
cooled,  the  cooling  being 
effected  by  a  natural  circu- 
lation of  air  up  over  the 
ice  and  down  through  the 
cold-storage  compartment. 
Were  the  ice  stored  in  a 
bunker  of  the  form  of  a  tank 
without  one  side  removed  it  is  obvious  that  the  heavy  cold  air,  like 
water,  would  sink  to  the  bottom  of  the  tank  and  there  would  be  lit- 
tle or  no  circulation.  If,  on  the  other  hand,  both  sides  of  the  tank 
are  removed  it  is  equally  obvious  that  the  tendency  would  be  for 
the  cold  air  to  flow  off  the  ice  in  both  directions.  This  would  give 
rise  to  conflicting  currents  of  air  which  would  check  the  circulation, 
and  for  the  same  rate  of  air  circulation  would  require  a  greater 
difference  in  temperature  between  the  air  in  the  bunker  and  that 
in  the  cooler  below. 

Natural  circulation  of  air  in  a  cold-storage  compartment  may 
be  compared  to  natural  draft  in  a  chimney  except  that  the  pur- 
pose and  the  causes  are  reversed.  In  the  case  of  natural  draft,  air 
and  gases  are  artificially  heated  in  a  furnace.  Since  the  heat 
causes  a  given  volume  to  expand  to  a  greater  volume,  its  weight 


Fig.  1. — Refrigerator  Cooled  by  Ice 
Bunker 


COMMERCIAL  SYSTEMS  OF  REFRIGERATION       19 

per  unit  of  volume  is  decreased,  causing  it  to  rise  in  the  cooler, 
heavier  air  above,  just  as  a  piece  of  cork  or  any  comparatively 
light  substance  rises  in  water. 

In  the  case  of  natural  circulation  of  air  in  a  cold-storage  com- 
partment the  air  is  artificially  cooled  in  a  bunker  containing  ice, 
or  some  other  cooling  means.  Since  the  extraction  of  heat,  or 
cooling,  causes  a  given  volume  to  contract  to  a  lesser  volume,  its 
weight  per  unit  of  volume  is  increased,  causing  it  to  sink  in  the 
lighter  air  of  the  cooler  below,  just  as  a  stone  or  any  heavy  sub- 
stance sinks  in  water. 

Since  both  the  bunker  and  the  room  below  are  completely 
filled  with  air  the  sinking  of  the  cold  air  on  one  side  can  take  place 
only  by  the  displacement  of  an  equal  volume  of  warm  air,  which 
rises  and  passes  into  the  bunker  on  the  other  side.  The  flow  of  air 
known  as " draft"  in  a  chimney,  "air  circulation"  in  a  cold  storage 
compartment,  or  "wind"  on  the  surface  of  the  earth,  takes  place 
only  because  of  a  difference* in  pressures  due  to  a  difference  in 
temperature.*  To  ensure  this  maximum  "draft"  or  "air  circu- 
lation" it  is  necessary  to  maintain  a  liberal  difference  in  tempera- 
ture and  a  reasonable  "head."  In  the  case  of  chimneys  this  is 
accomplished  by  so  constructing  the  walls  as  to  prevent  undue 
radiation  of  heat  and  of  such  a  height  as  to  give  a  difference  in 
weight,  equal  to  the  required  draft,  between  the  hot  air  within  and 
the  cold  air  without  the  chimney.  Similarly,  in  the  case  of  the 

*  Since  the  difference  in  temperature  is  greater,  production  of  draft  in  a 
chimney  furnishes  the  better  example. 

The  difference  in  weight  per  cubic  foot  between  air  at  62°  Fahrenheit  and 
500°  Fahrenheit  is  0.0761-0.0413  =  0.0348  pound.  A  column  of  62°  air  100 
feet  high  would  accordingly  weigh  7.61  pounds,  and  an  equal  column  of  500° 
air,  4.13  pounds,  making  a  difference  in  weight  of  7.61—4.13=3.48  pounds. 
If  the  column  of  500°  air  be  in  a  chimney  100  feet  high,  and  the  62°  air  out- 
side, the  actual  difference  in  pressure  tending  to  produce  upward  flow  of  air 
in  the  chimney  will  be  3.48  pounds  per  square  foot,  or  16X3.48 -=-144  =  0.3866 
ounces  per  square  inch.  Chimney  draft  is  usually  expressed  in  inches  of  water. 
Water  at  62°  Fahrenheit  weighs  62.32  pounds  per  cubic  foot.  The  pressure 
due  to  a  column  of  water  1  foot  high  is  accordingly  62.32  pounds  per  square 
foot.  The  pressure  in  ounces  per  square  inch  due  to  a  column  of  water  one 
inch  high  is  62.32X16-7-  (144X12)  =0.577.  The  difference  in  pressure  of 
0.3S66  ounces  per  square  inch,  due  to  the  100-foot  stack  and  a  difference  in 
temperature  of  500-62°  Fahrenheit  would  accordingly  be  equivalent  to 
0.3866-j-0.577  =  0.67  inches  of  water;  or  since  the  specific  gravity  of  mercury 
is  13.58  (13.58  times  the  weight  of  water)  the  draft  as  expressed  in  inches  of 
mercury  would  be  0.674-13.58=0.049. 


20    ELEMENTARY  MECHANICAL  REFRIGERATION 

cold-storage  bunker  the  uptakes  should  be  insulated  to  prevent 
the  cooling  of  the  rising  column  of  warm  air  and  the  height  of  the 
cooler  compared  to  the  width  between  hot  and  cold  air  ducts 
should  be  kept  as  great  as  possible. 

BUNKER  INSULATION 

To  prevent  the  cooling  of  the  air  lying  next  to  the  floor  in  the 
bunker,  which  not  only  retards  circulation  by  reducing  the  dif- 
ference in  temperature,  but  may  also  precipitate  moisture  when 
the  warm  air  approaches  saturation,  the  bunker  floors  should  also 
be  insulated.  When  operating  with  properly  insulated  bunkers  and 
liberal  ducts,  the  circulation  should  be  sufficiently  rapid  to  carry 
away  any  moisture-saturated  air  that  may  enter  the  cooler  from 
the  outside  or  that  may  have  become  saturated  through  contact 
with  stored  products,  to  the  ice  chamber  before  its  moisture  can 
be  precipitated  by  contact  with  the  cold  surfaces  of  the  cooler. 
When  cooled  in  this  way  the  excess  moisture  is  precipitated  in  the 
ice  bunker  and  flows  away  with  the  melted  ice. 

Where  the  warm  air  ducts  or  the  bunker  floors  are  not  insu- 
lated, excess  dampness  can  be  prevented  only  by  the  use  of  some 
such  deliquescent  salt  as  calcium  chloride.  This  is  the  case  when 
the  air  of  the  cooler  is  not  allowed  to  come  in  contact  with  the 
melting  ice  but  is  chilled  by  contact  with  the  metallic  floors  of 
overhead  bunkers  or  the  walls  of  tank  bunkers. 

Where  salt  is  used  so  that  the  resulting  temperatures  are  below 
freezing,  the  precipitated  moisture  is  frozen  on  the  heat-absorbing 
surfaces  and  the  difficulties  arising  from  condensation  are  avoided, 
but  in  time  the  accumulated  ice  has  to  be  removed,  giving  rise  to 
other  difficulties. 

Exceptionally  well  insulated  coolers  have  been  constructed 
in  which  it  is  possible  to  maintain  temperatures  as  low  as  from 
38°  to  40°  Fahrenheit  in  compartments  cooled  by  natural  cir- 
culation and  ice  without  the  use  of  salt.  The  average  cooler,  how- 
ever, is  not  capable  of  producing  such  favorable  temperatures, 
and  the  present-day  demand  for  lower  temperatures  makes  it 
necessary  to  resort  to  other  means.  The  addition  of  salt  allows 
the  natural  circulation  and  ice  system  to  satisfy  a  few  such  re- 
quirements, and  the  further  addition  of  a  fan  to  force  the  circu- 
lation may  allow  it  to  include  a  few  more. 


COMMERCIAL  SYSTEMS  OF  REFRIGERATION      21 

GRAVITY  BRINE  SYSTEM 

For  still  further  extending  the  application  of  ice  cooling,  the 
system  illustrated  in  Fig.  2  has  been  devised.  This  system  con- 
sists essentially  of  a  tank  for  holding  the  ice  and  salt  in  the  pro- 
portion required  to  produce  the  desired  temperatures,  and  a  con- 
tinuous pipe  circuit,  a  part  of  which  is  located  in  the  cold-storage 
compartment,  where  it  absorbs  heat,  and  the  other  part  in  the  ice 
tank,  where  it  gives  up  heat  to  the  ice  or  freezing  mixture  of  ice 
and  salt,  as  the  case  may  be.  The  pipe  is  filled  with  brine  of  just 


Fig.  2. — Refrigerator  Cooled  by  Gravity 
Brine  System 


sufficient  density  to  insure  against  freezing.  The  brine  in  the  coil 
of  pipe  located  in  the  tank,  becoming  heavier  as  it  is  cooled  by  the 
surrounding  ice  and  salt,  flows  down  into  the  coil  located  in  the 
cold-storage  compartment,  causing  the  warmer,  lighter  brine  to 
pass  upward  and  take  its  place  in  the  ice  tank.  Heat  is  conveyed 
from  the  cold-storage  compartment  to  the  ice  chamber  by  the 
natural  circulation  of  the  conveying  medium  as  in  the  preceding 
cass,  but  in  this  case  the  medium  is  a  liquid,  brine,  while  in  the  pre- 
ceding one  it  was  a  gas,  air.  An  abnormal  rise  in  temperature  of 
the  cooler  increases  the  velocity  of  the  brine  circulation  and  con- 
sequently increases  the  refrigerating  capacity  of  the  system.  By 
the  use  of  this  system  it  is  possible  to  prevent  the  air  of  the  cold- 


22    ELEMENTARY  MECHANICAL  REFRIGERATION 

storage  compartment  from  becoming  contaminated  by  contact 
with  melting  ice  and  unsanitary  ice  bunkers. 

ELEMENTARY  MECHANICAL  SYSTEMS — DIRECT  EXPANSION 

When  the  refrigerating  fluid  is  a  condensable  gas,  or,  more 
accurately  speaking,  a  liquid  having  a  sufficiently  low  boiling 
point  to  evaporate  and  absorb  heat  under  conveniently  low  pres- 
sures to  produce  the  desired  temperatures  the  process  of  mechan- 
ical refrigeration  may  be  explained  as  follows: 


!Fig.     3. — Elementary    Direct-Expansion 
System 

Fig.  3  represents  a  flask  partly  filled  with  a  refrigerant  such  as 
anhydrous  ammonia.  Since  the  pressure  on  the  refrigerant  in  the 
open  flask  is  only  that  of  the  atmosphere,  it  will  boil  at — 28.5° 
Fahrenheit.  As  this  temperature  is  far  below  that  of  the  sur- 
rounding air  under  usual  conditions,  heat  will  pass  from  the 
air  into  the  refrigerant;  the  former  will  be  refrigerated  and  the 
latter  heated  up  to  the  boiling  point,  if  it  is  not  already  boiling. 
At  the  boiling  point  the  absorption  of  a  definite  amount  of  heat 
from  the  air  effects  the  evaporation  of  a  definite  amount  of  the 
liquid;  the  anhydrous  ammonia,  absorbing  heat  directly  through 
the  walls  of  the  containing  vessel  from  the  surrounding  air,  oper- 
ates just  as  it  and  similar  refrigerating  media  do  in  the  direct- 
expansion  refrigerating  system.  This  cooling  effect  is  hastened 
by  a  marked  circulation  of  air  around  the  flask,  occasioned  by  the 


COMMERCIAL  SYSTEMS  OF  REFRIGERATION     23 

greater  specific  gravity  or  weight  of  the  cooled  film  of  air  lying 
next  to  the  flask,  which  flows  down  and  away  at  the  bottom,  caus- 
ing the  warmer  air  to  rise  and  take  its  place  at  the  top. 

BRINE  CIRCULATION  SYSTEM 

The  brine  system  has  its  elementary  counterpart  in  such  an 
arrangement  as  is  illustrated  in  Fig.  4,  in  which  the  flask  contain- 
ing the  boiling  anhydrous  ammonia  is  immersed  in  a  second  vessel, 
such  as  a  large  beaker,  filled  with  a  brine  solution  of  sodium 


Jig.  4. — Elementary  Brine  System 

chloride  (NaCl),  calcium  chloride  (CaCl),  or  other  salt  in  water. 
The  low  first  cost,  together  with  certain  physical  and  chemical 
characteristics,  has  practically  limited  the  commercial  brine  sys- 
tem to  the  use  of  either  sodium  or  calcium  chloride  solutions. 
As  in  the  preceding  case,  the  boiling  refrigerating  medium  absorbs 
heat  from  the  surrounding  medium,  in  this  case  brine,  which  we 
will  assume  is  of  such  a  nature  as  not  to  freeze  at —  28.5°  Fahren- 
heit. Since  this  solution  does  not  freeze  at  the  temperature  of  the 
evaporating  refrigerant,  and  the  latent  heat  of  fusion  of  the  liquid 
is  not  extracted,  an  evaporation  of  only  a  comparatively  small 
amount  of  the  refrigerant  suffices  to  cool  the  surrounding  solution 
almost  down  to  —28.5°  Fahrenheit.  This  cooling  effect  is  has- 
tened by  a  marked  circulation  within  the  solution  itself,  set  up  by 
the  difference  in  specific  gravity  of  the  colder  part  of  the  liquid 


24    ELEMENTARY  MECHANICAL  REFRIGERATION 


lying  next  to  the  flask,  which  sinks  to  the  bottom  of  the  beaker, 
causing  the  warmer  part  to  flow  in  and  take  its  place  at  the  top. 

The  brine  in  the  beaker  having  become  colder  than  the  sur- 
rounding air,  heat  flows  from  the  air  to  the  brine,  just  as  it  flowed 
from  the  air  to  the  ammonia  in  the  preceding  case.  It  will  be 
noted,  however,  that  difference  in  temperature,  and  accordingly 
the  flow  of  heat,  between  the  air  and  the  brine  can  never  be  so 
rapid  as  that  between  the  air  and  the  ammonia,  except  in  the 
limiting  case  in  which  the  brine  and  the  ammonia  are  of  the  same 
temperature,  when,  unfortunately,  the  ammonia  would  have  no 
cooling  effect  on  the  brine.  If  the  same  amount  of  the  same  re- 
frigerant be  placed  in  flasks  of  the  same  shape  and  size  in  both 
the  foregoing  experiments,  it  will  be  found  that  the  brine  employed 
in  the  second  case  will  assume  a  temperature  intermediate  between 
that  of  the  boiling  ammonia  and  that  of  the  surrounding  air,  and 
were  there  any  way  to  measure  the  cooling  effect  produced  on  the 
air,  it  would  probably  be  found  that  less  heat  would  be  absorbed 
in  the  latter  than  in  the  former  case,  notwithstanding  the  fact 
that  the  heat-absorbing  surface  of  the  beaker  is  greater  than  that 
of  the  flask.  A  very  crude  idea  of  this  difference  might  be  gained 
by  surrounding  the  vessels  used  in  each  experiment  by  boxes  made 
of  the  same  size  and  material  and  noting  the  temperature  of  the 
air  within. 

The  flasks  containing  the  ammonia  employed  in  the  above 
examples  correspond  to  the  expansion  pipes  immersed  in  and 
employed  for  the  purpose  of  cooling  the  brine  in  the  brine  system 

described  below,  and  the  beaker  con- 
taining the  brine,  to  the  brine  pipes 
immersed  in  and  employed  for  cooling 
the  air  in  the  cold-storage  compart- 
ments. 

ICE  FREEZING  SYSTEM 

If  the  flask  of  ammonia  employed 
in  the  second  experiment  had  been  im- 
mersed in  water,  as  shown  in  Fig.  5, 
instead  of  brine,  as  shown  in  Fig.  4, 
the  water  which  freezes  under  atmos- 
pheric pressure  at  32°  Fahrenheit,  will 
give  up  first  its  specific  heat  in  cooling, 


Fig.  5. — Elementary  Ice 
Freezing  System 


COMMERCIAL  SYSTEMS  OF  REFRIGERATION     25 

then  its  latent  heat  in  freezing,  to  the  anhydrous  ammonia  boiling 
under  atmospheric  pressure  at  —28.5°  Fahrenheit,  with  the  result 
that  the  water  will  first  be  cooled  from  its  initial  temperature  to 
32°  Fahrenheit,  then  be  frozen  at  32°.  If  sufficient  ammonia  still 
remains  and  heat  is  not  absorbed  too  rapidly  from  the  surrounding 
air,  the  ice  will  be  cooled  to  several  degrees  below  32°;  in  fact, 
that  part  lying  nearest  the  flask  may  be  chilled  to  the  temperature 
of  the  evaporating  liquid,  —28.5°  Fahrenheit.* 

COMMERCIALLY  PRACTICAL  SYSTEM 

Were  it  not  for  the  initial  cost  of  the  refrigerating  medium, 
this  elementary  refrigerating  system  in  which  the  ammonia  is 
allowed  to  escape  to  the  atmosphere  after  evaporation  might  find 
commercial  application,  but  since  anhydrous  ammonia  commands 
a  practically  fixed  market  price  of  $0.25  and  upward  per  pound, 
according  to  the  distance  from  point  of  production,  such  a  system 
would  be  eminently  impracticable. 

In  order,  therefore,  to  make  the  systems  illustrated  in  Figs. 
3,  4,  5,  and  6  commercially  practicable,  means  must  be  provided 
for  converting  the  gasified  anhydrous  ammonia  back  into  the 
liquid  state.  A  commercial  refrigerating  system  is  simply  a  con- 
venient mechanical  means  for  circulating  a  heat-absorbing  medium 
through  the  cooler,  and  of  removing  from  this  medium  the  heat 
absorbed  en  route.  Heat  is  absorbed  in  the  cooler  from  the  atmos- 
phere, products,  etc.,  by  virtue  of  the  fact  that  the  refrigerating 
medium  is  lower  in  temperature.  This  absorption  of  heat  brings 
about  evaporation  and  before  the  refrigerant  can  be  made  to  do 

*If  a  pound  of  anhydrous  ammonia  be  evaporated  from  and  at  —  28.5° 
Fahrenheit  in  the  flask,  the  amount  of  heat  which  it  will  absorb  will  be  573 
B.t.u.,  which  is  its  latent  heat  of  vaporization.  If  now  it  be  assumed  that  this 
heat  is  all  drawn  from  three  pounds  of  water  at  an  initial  temperature  of  79° 
Fahrenheit,  it  will  just  suffice,  assuming  no  losses,  to  cool  it  down  to  the  freez- 
ing point  and  then  to  freeze  it  at  32°  Fahrenheit,  47  B.t.u.  for  each  of  the  three 
pounds  being  required  to  overcome  the  specific  heat  of  the  water  in  cooling 
it  through  47  degrees,  and  144  B.t.u.  for  each  pound  of  water  at  32°  Fahrenheit 
being  required  to  overcome  the  latent  heat  of  fusion. 

Three  pounds  water  X  drop  in  temperature  from  79  to  32  degrees 
X  specific  heat  of  water  (unity)  +  three  pounds  water  X  latent  heat  of 
fusion  of  water  (144  B.t.u. )=latent  heat  of  vaporization  of  the  am- 
monia (573  B.t.u.)  required  to  cool  and  freeze  the  three  pounds  of 
water. 

3X1(79 -32)+ 3X144=573. 


26    ELEMENTARY  MECHANICAL  REFRIGERATION 


more  cooling  work  it  must  be  again  liquefied.  In  other  words,  after 
the  ammonia  has  evaporated  and  has  absorbed  its  full  complement 
of  heat,  much  as  the  sponge  sucks  up  its  fill  of  water,  the  heat  and 
water  with  which  the  ammonia  and  a  sponge  are  respectively 
charged  must  be  squeezed  out  before  they  can  again  perform  the 
function  of  absorption.  In  the  case  of  the  sponge,  this  is  accom- 
plished by  the  simple  application  of  pressure.  In  the  case  of 

* 


Fig.  6. — Expansion  Side  of  Elementary  Brine  System 

ammonia,  pressure  must  not  only  be  applied,  but,  since  heat  can 
be  made  to  flow  only  from  a  relatively  warmer  to  a  relatively  cooler 
substance,  some  cooling  medium  must  be  provided  as  well.  The 
two  cheapest  and  otherwise  most  convenient  natural  cooling  media 
we  have  at  our  command  are  air  and  water.  On  account  of  the  low 
specific  heat  of  the  former  and  the  fact  that  it  is  usually  at  a  higher 
temperature  than  water  found  in  the  same  locality,  we  are  practi- 
cally limited  to  the  use  of  water. 

If  carried  out  in  an  ice  plant  instead  of  a  laboratory,  the  appa- 
ratus requisite  for  the  above  experiments  would  probably  appear 
more  nearly  as  in  Fig.  6.  In  this  illustration  the  glass  flask  is  re- 
placed by  an  iron  flask,  or  drum,  such  as  is  commonly  used  for 


COMMERCIAL  SYSTEMS  OF  REFRIGERATION      27 

shipping  ammonia,  carbon-dioxide,  and  other  liquefied  gases.    The 

liquid  from  this  flask  is  allowed  to  "expand"  or  escape  in  a  small 

stream  through  a  valve  V 

and  a  pipe  leading  to  an  ex-  <  Expansion      v 

pansion  coil.   After  travers-  *— 

ing  this  coil,  the  vaporized  V- 

ammonia    escapes    to   the 

atmosphere.     This    outlet,  V_ 


however,  is  provided  with  Receiver  i JL 

a    valve    V,  which,    when      1  >  I    ^ 

closed,  diverts  the  ammonia        

through  a  spmnd  nine  with     Fig'    6&'~ Conventionalized   Diagram   of 

Expansion   Side  of  Elementary  Brine 
two  outlets,  each  provided       System 

with  a  valve,  the  one  lead- 
ing to  a  tank  of  water  and  the  other  to  an  ammonia  compressor.  If 
diverted  into  the  water,  the  ammonia  vapor  will  be  absorbed  and 
be  recoverable  in  the  form  of  aqua  ammonia,  a  principle  which, 
as  will  be  shown  later,  is  employed  in  the  absorption  type  of  re- 
frigerating machine.  If  conducted  to  an  ammonia  compressor 
and  suitable  condenser,  it  may  be  condensed  and  recovered  in  the 
form  of  anhydrous  ammonia,  a  principle  which  is  employed  in  the 
compression  type  of  refrigerating  system.  The  several  parts  used 
in  commercial  refrigerating  systems  to  take  the  place  of  those 
illustrated  in  Figs.  3,  4  and  5  are  represented  diagrammatically 
in  the  figures  that  are  to  follow.  Fig.  66  is  such  a  conventional 
representation  of  an  ammonia  flask  or  receiver,  a  controlling  or 
expansion  valve  V  and  a  container  of  the  boiling  liquid  ammonia, 
or  expansion  coil,  which  may  be  connected  to  any  type  of  device 
for  converting  the  vaporized  refrigerant  back  into  the  liquid  state. 
Before  this  can  be  accomplished,  however,  the  heat  absorbed  in  the 
cold-storage  rooms  must  be  squeezed  out,  or  rather  be  induced  to 
flow  out,  of  the  refrigerating  medium  by  introducing  a  secondary 
medium  materially  lower  in  temperature.  Since  there  is  no  sec- 
ondary cooling  medium  available  of  a  lower  temperature  than  the 
refrigerating  medium,  even  at  the  temperature  at  which  it  returns 
from  the  cooler  after  having  absorbed  large  quantities  of  heat,  it 
becomes  necessary  to  raise  the  temperature,  or  thermal  level,  of 
the  heat  in  the  refrigerating  medium  above  that  of  the  cooling 
medium  sufficiently  to  allow  it  to  gravitate  into  the  cooling  water. 
Were  the  water  sufficiently  cold,  i.e.,  colder  than  the  gaseous 


28    ELEMENTARY  MECHANICAL  REFRIGERATION 

ammonia  returning  from  the  cooler,  the  flow  would  take  place 
without  the  increase  in  pressure  and  temperature,  and  there  would 
be  no  need  for  a  compressor.  On  the  other  hand,  if  so  cold  a  medium 
were  available,  it  would  be  used  directly  for  absorbing  heat  in  the 
place  of  the  ammonia  or  the  ammonia  and  brine,  as  it  would  then 
be  sufficiently  cold  to  induce  a  flow  of  heat  direct  from  the  products 
to  be  refrigerated. 

ESSENTIAL  MEMBERS  OF  COMMERCIAL  SYSTEMS 

A  commercial  refrigerating  system  consists  of  a  set  of  pipes, 
or  other  containing  vessels,  in  the  cooler,  in  which  the  refrigerating 
medium  absorbs  heat  at  a  low  temperature  from  the  products  to 
be  refrigerated;  a  second  set  of  pipes,  or  other  containing  vessel, 
outside  of  the  cooler  in  which  the  refrigerating  medium  gives  up 
its  heat  to  a  secondary  cooling  medium,  such  as  water  or  air,  at  a 
comparatively  high  temperature;  and  a  compressor  or  generator. 

The  pipes  located  in  the  cooler,  through  the  walls  of  which  the 
ammonia  absorbs  heat  from  the  objects  to  be  refrigerated,  are 
erroneously  called  expansion  coils,  and  those  through  the  walls  of 
which  the  ammonia  gives  up  its  heat  to  the  natural  cooling  me- 
dium, water,  condenser  coils. 

Since  the  pressure  and  consequent  temperature  of  the  cold 
ammonia  gas  returning  from  the  expansion  pipes  must  be  raised 
before  a  heat  transfer  can  be  made  to  take  place  between  it  and 
cooling  water  at  ordinary  temperatures,  the  use  of  a  compressor 
or  suitable  gas  pump,  in  the  case  of  the  compression  system,  and 
some  other  means  of  heating  and  increasing  the  pressure  of  the 
refrigerating  medium,  in  case  of  the  absorption  system,  must  be 
employed.  In  either  system  there  must  also  be  provided  a  suitable 
cooling  chamber  or  condenser  in  which  the  cooling  water  can  be 
brought  in  sufficiently  close  proximity  to  the  refrigerating  medium 
to  allow  the  necessary  heat  flow  from  the  hot  ammonia  to  the  cold 
water  to  take  place. 

In  practice,  this  operation  is  effected  as  follows:  Ammonia, 
for  example,  boils,  evaporates,  and  liquefies  under  a  pressure  of 
16  pounds  at  a  temperature  of  0°.  In  changing  from  the  liquid  to 
the  gaseous  state  it  absorbs,  and  from  the  gaseous  to  the  liquid 
state,  it  gives  up  an  amount  of  heat  equivalent  to  its  latent  heat 
of  vaporization,  for  it  must  be  understood  that  liquefaction  of  a 
vapor  at  the  boiling  point  of  the  substance  may  be  effected  just 


COMMERCIAL  SYSTEMS  OF  REFRIGERATION      29 

as  readily  by  cooling  as  vaporization  can  by  heating,  the  only 
difference  in  conditions  being  that  it  is  necessary  to  provide  a 
colder  medium  to  absorb  heat  from  the  gas  in  the  latter  case, 
whereas  a  warmer  one  was  employed  to  supply  heat  to  the  liquid 
in  the  former  case.  This  reversible  operation  of  vaporization  and 
liquefaction  may  in  the  general  case  take  place  at  any  temperature 
and  its  corresponding  pressure. 

As  there  is  no  natural  cooling  medium  cold  enough  to  liquefy 
a  refrigerating  medium  such  as  ammonia  gas,  for  example,  at  the 
temperature  at  which  it  comes  from  the  cooler,  its  temperature 
must  be  increased.  As  water  is  a  natural  cooling  medium,  the 
temperature  of  the  refrigerant  is  usually  raised  to  a  few  degrees 
above  the  temperature  of  that  medium.  In  other  words,  to  effect 
the  extracting  of  heat  from  the  refrigerant  by  air  or  water,  it  is 
necessary  to  shift  the  boiling  point  of  the  medium  from  that  of 
the  cooler  to  some  temperature  a  few  degrees  higher  than  that  of 
the  condenser.  This  is  the  purpose  of  the  generator  of  the  absorp- 
tion, and  the  compressor  of  the  compression  system.  By  the  direct 
application  of  heat  in  the  former  and  power  in  the  latter,  the  pres- 
sure and  temperature  of  the  refrigerant  vapor  is  increased  just  as 
the  pressure  of  steam  is  increased  by  the  application  of  heat 
under  a  boiler  and  by  compression  in  a  steam  cylinder  at  the  end 
of  the  exhaust  stroke.  • 

If  the  temperature  of  the  available  cooling  water  be  80°  it  will 
be  necessary  to  raise  the  temperature  of  the  vapor  to  say  100°  in 
order  to  provide  a  sufficient  difference  in  temperature  to  carry  out 
the  cooling  effect. 

In  the  case  of  anhydrous  ammonia  above  cited,  the  original 
and  final  temperatures  and  corresponding  pressures  are  as  follows : 

Cooler  Temp.,  0°;  Cooler  or  "Back"  Pres.,  16  Ibs. 

Condenser  Temp.,  100°;     Condenser  or  "Head"  Pres.,        200  Ibs. 

WORKING  MEDIUMS 

In  the  operation  of  a  compression  system,  almost  any  gaseous 
working  medium  might  be  employed.  In  practice,  however,  the 
list  is  limited  to  only  such  gases  as  are  capable  of  being  liquefied 
under  ordinary  natural  temperatures  and  not  to  high  mechani- 
cally produced  pressures.  Judging  from  the  relative  number  of 
commercial  installations  employing  the  different  media,  one  may 
assume  that  under  the  average  conditions  anhydrous  ammonia 


30    ELEMENTARY  MECHANICAL  REFRIGERATION 


comes  nearer  to  fulfilling  all  the  requirements  of  a  practical  work- 
ing medium  than  any  other. 

The  system  described  and  illustrated  in  Fig.  3  consists 
essentially  of  a  single  member,  i.e.,  a  containing  vessel  for  the 
working  medium.  Here  there  is  no  outer  containing  vessel 
and  no  second  liquid.  In  this  case  the  heat  passes  from  the 
air  surrounding  the  flask,  directly  to  the  ammonia,  just  as  the  air 
of  a  cold-storage  compartment  is  cooled  by  "  direct  expansion," 
a  system  which  is  differentiated  from  the  brine  system  by  the 


7 


w 


C 


Fig.  7. — Direct-Expansion — Compression  Refrigerating  System 

location  of  the  " expansion  coils"  containing  the  boiling  or  expand- 
ing ammonia,  in  direct  contact  with  the  atmosphere  of  the  cold- 
storage  rooms. 

The  commercial  system  corresponding  to  the  one  illustrated 
in  Fig.  4,  in  which  the  evaporation  of  the  ammonia  cools  the  sur- 
rounding water,  which  in  turn  cools  the  surrounding  air,  is  the 
"brine  system,"  which  takes  its  name  from  the  fact  that  the  cool- 
ing effect  of  the  refrigerating  medium  is  expended  on  a  more  or 
less  uncongealable  solution,  such  as  sodium  chloride  (NaCl)  or 
calcium  chloride  (CaCl)  brine,  in  which  the  cooling  solution  cir- 
culated through  a  secondary  system  of  cools  in  the  cold-storage 
compartments  is  made  the  vehicle  for  conveying  the  refrigeration 
to,  or,  more  properly  speaking,  the  heat  away  from,  the  atmos- 
phere in  the  cold-storage  rooms. 

THE  DIRECT-EXPANSION  COMPRESSION  SYSTEM 

Fig.  7  is  a  diagrammatic  representation  of  the  essential  mem- 
bers of  a  complete  compression  refrigerating  system.  E  represents 
the  direct-expansion  coil  in  which  the  working  medium  is  evapo- 


COMMERCIAL  SYSTEMS  OF  REFRIGERATION      31 


rated  as  in  the  flask,  P  the  compressor  or  pump  for  increasing  the 
pressure  of  the  gasified  ammonia,  C  the  condenser  for  cooling  and 
liquefying  the  gasified  ammonia,  and  V  a  throttling  valve  by  which 
the  flow  of  liquefied  ammonia  under  condenser  pressure  is  con- 
trolled as  it  flows  from  the  receiver  R  to  the  expansion  coil  E}  in 
which  a  materially  lower  pressure  is  maintained  by  the  pump  in 
order  that  the  refrigerating  medium  may  boil  at  a  sufficiently  low 
temperature  to  absorb  heat  from  and  consequently  refrigerate  the 
surrounding  air,  which  is  already  cold.  In  practice,  the  systems 
are  somewhat  more  elaborate,  Fig.  15  being  a  more  accurate 
representation  of  a  commercial  system  as  applied  to  the  direct 
cooling  of  cold-storage  compartments. 

BRINE  CIRCULATING  SYSTEM 

In  order  that  some  work  of  refrigeration  may  be  carried  on 
while  the  plant  proper  is  shut  down  either  because  of  accident  or 


Fig.  8. — Brine-Circulation — Compression  Refrigerating  System 

in  order  to  avoid  the  expense  of  skilled  attendance  during  a  part  of 
the  twenty-four  hours,  the  brine-circulating  system  is  employed. 
Such  a  system  is  represented  in  the  conventionalized  diagram,  Fig. 
8.  In  addition  to  the  usual  members  of  the  direct-expansion  refrig- 
erating system  represented  in  Fig.  1,  the  brine  system  employs  a 
brine  tank  T,  a  series  of  air-cooling  or  brine  coils  and  a  brine  pump 
B.  P.  In  this  case  the  initial  cooling  effect  of  the  evaporating 
ammonia  is  expended  in  the  brine  which  is  circulated  by  the  brine 
pump  through  the  air-cooling  coils  installed  in  the  cold-storage 
room  R. 

Salt,  either  sodium  chloride  (NaCl)  or  calcium  chloride  (CaCl)  is 
required  for  making  the  brine,  and  suitable  insulation  must  be 
provided  for  the  brine  tank,  the  brine  cylinders  of  the  pump  and 
all  brine  piping  outside  of  the  cold-storage  compartments  in  order 


32    ELEMENTARY  MECHANICAL  REFRIGERATION 

to  reduce  to  a  minimum  the  losses  due  to  the  radiation  of  cold, 
or  more  accurately  speaking,  the  absorption  of  heat.  In  addition 
to  the  first  cost  of  the  above-mentioned  items,  the  operating  ex- 
pense or  power  required  to  operate  the  brine  pump  must  be  con- 
sidered; first,  for  the  circulation  of  brine  from  the  brine  tank 
through  the  cooling  coils  back  to  the  tank;  second,  to  overcome 
the  friction  of  the  brine  in  traversing  the  above  cycle;  third,  to 
produce  sufficient  additional  refrigeration  to  make  up  for  the 
heating  effect  produced  mechanically  by  the  circulation  of  brine 
and  the  heat  actually  absorbed  through  the  brine  tank  and  brine- 
piping  insulation;  and  fourth,  to  make  up  for  the  greatly  reduced 
efficiency  occasioned  by  the  necessity  of  operating  the  refrigerating 
plant  proper  at  a  materially  lower  back  pressure  in  order  to  pro- 
duce a  sufficiently  lower  ammonia  temperature  to  make  up  for  the 
second  heat  transfer  encountered  between  the  atmosphere  of  the 
cold-storage  compartments  and  the  ammonia  gas.  The  increased 
operating  expense  directly  resulting  from  the  inherent  low  effi- 
ciency of  the  brine  system  is  sometimes  as  high  as  25  per  cent., 
and  isolated  instances  have  been  noted  in  small  plants  where  the 
cost  of  circulating  the  brine  alone  was  almost  as  great  as  that  of 
cooling  it. 

CONGEALING  TANK  SYSTEM 

Instead  of  the  brine  system  some  builders  employ  what  is 
known  as  the  "  congealing-tank "  system,  represented  diagram- 
matically  in  Fig.  9.  The  first  cost  of  the  brine  pump  and  the  power 
required  to  operate  it,  and  the  cost  of  brine  pipe  and  tank  insu- 
lation, as  well  as  the  losses  through  the  same,  are  avoided  in  this 
system  by  virtually  splitting  up  the  main  brine  tank  and  installing 
the  pieces  commonly  called  " congealing  tank"  in  the  several  cold- 
storage  compartments.  In  this  case  the  heat-absorbing  surface 
of  the  several  smaller  tanks  entirely  replaces  that  of  the  brine 
coils.  Here,  however,  the  desirability  from  a  mechanical  stand- 
point of  making  the  tanks  as  small  as  possible  debars  the  carrying 
of  sufficiently  large  volumes  of  brine  to  provide  for  refrigerating 
the  rooms  for  any  great  length  of  time  by  the  rise  in  temperature 
only  of  the  brine.  The  amount  of  refrigeration  performed  meas- 
ured in  B.t.u.  would  be  the  product  of  the  pounds  of  brine,  the 
number  of  degrees  rise  in  temperature  and  the  specific  heat  of  the 
brine: 

B.t.u.  =  Ib.  brine  X  specific  heat  of  brine  X  (t— fr). 


COMMERCIAL  SYSTEMS  OF  REFRIGERATION     33 


In  order  to  store  more  refrigeration  in  the  comparatively  small 
volume  of  the  congealing  tanks  a  weak  solution  of  brine  is  em- 
ployed, which,  in  freezing,  stores  refrigeration  proportional  to  the 


w 


Fig.  9. — Congealing  Tank — Compression  Refrigerating  System 


number  of  pounds  of  brine  frozen  multiplied  by  the  latent  heat 
of  fusion  of  the  brine  ice  plus  the  cold  required  to  chill  the  brine 
down  to  the  freezing  point : 


B.t.u.  =  Ib.  ice  x  \  latent  heat+[specific  heat  of  brine  x  (t  —  h)] 


This  expression  does  not  provide  for  the  small  additional 
amount  of  refrigeration  required  to  cool  the  brine-ice  below  its 
freezing  point.  When  the  temperature  of  the  ice  is  below  the 
freezing  point  the  additional  refrigeration  will  be  found  from  the 
expression 

B.t.u.  =  Ib.  ice  xspecific  heat  of  the  ice  x  ft  —  &)• 

In  the  above  expressions  t  is  the  temperature  of  the  brine  before 
cooling,  ti  the  temperature  at  which  the  brine  freezes  and  £3  the 
temperature  to  which  the  ice  is  cooled  after  freezing. 

In  order  that  the  rooms  may  be  cooled  more  quickly  when  the 
refrigerating  plant  resumes  operation  after  several  hours  of  in- 
action, it  is  often  desirable  to  install  from  one-third  to  two- 
thirds  of  the  total  expansion  piping  outside  the  tanks  in  direct 
contact  with  the  atmosphere  of  the  rooms,  the  remaining  two- 
thirds  or  one-third  being  submerged  in  the  weak  brine  of  the  con- 
gealing tanks. 

It  is  evident  from  the  foregoing  that  so  far  as  decreased  effi- 
ciency entailed  by  the  double-heat  interchange  of  the  brine- 


34    ELEMENTARY  MECHANICAL  REFRIGERATION 

circulating  system  is  concerned,  the  congealing-tank  system  is 
only  a  compromise.  While  a  part  of  the  piping  cools  the  air  by 
direct  radiation,  the  greater  part  must  transmit  cold  first  to  the 
surrounding  brine,  or  ice,  as  the  case  may  be,  which  medium  in 
turn  must  transmit  it  on  through  the  walls  of  the  tanks  to  the  air; 
and  a  sufficiently  low  ammonia  evaporation  or  "back  pressure" 
with  its  entailed  loss  of  efficiency,  must  be  maintained  in  both  the 
submerged  and  the  exposed  coils,  to  carry  out  the  double-heat 
interchange  in  the  latter.  The  fact  that  the  refrigeration  stored 
up  during  the  hours  of  operation  of  the  plant  for  use  during  the 
hours  of  rest  is  in  the  form  of  a  coating  of  ice  on  the  coils,  instead 
of  brine  kept  in  constant  circulation,  further  increases  the  neces- 
sity for  a  lower  back  pressure;  first,  because  ice  is  a  poorer  con- 
ductor of  heat  than  brine;  second,  because  the  congealing-tank 
surface,  as  well  as  that  of  the  expansion  pipes,  is  often  insulated 
with  ice;  and  third,  because  the  stagnant  brine,  or,  what  is  even 
worse,  ice  in  the  case  of  the  congealing-tank  system,  absorbs  and 
gives  up  heat  less  readily  than  the  moving  brine. 

As  it  is  mechanically  impracticable  to  make  the  thin,  light 
congealing  tanks  indefinitely  continuous,  as  is  done  in  the  case  of 
ammonia  or  brine-cooling  coils,  the  ammonia-expansion  coils 
installed  in  such  tanks  must  be  made  shorter.  This  necessitates 
the  use  of  an  increased  number  of  return  bends  or  fittings  for  the 
installation  of  the  system  as  a  whole  and  accordingly  tends  to 
increase  the  initial  cost  of  the  expansion  piping  for  both  material 
and  labor. 

ELECTRICALLY  DRIVEN  PLANTS 

While  the  use  of  electric  power  undoubtedly  reduces  the  duties 
of  the  attendant,  safety  and  the  necessity  of  adjusting  expan- 
sion valves  by  hand  require  more  or  less  constant  attention,  and 
the  slight  additional  attention  required  by  the  steam  or  combus- 
tion engine  is  usually  too  slight  to  make  up  for  the  usual  compara- 
tively high  cost  of  electric  power. 

The  application  of  reliable  safety  devices,  however,  which 
protect  the  plant  in  case  of  abnormal  pressure  resulting  from 
failure  of  water  supply  or  the  accidental  closing  of  the  wrong 
valves,  together  with  a  reliable  automatic  expansion  valve,  elimi- 
nates these  two  most  important  duties  of  the  attendant.  When 
the  compressors  are  of  the  inclosed-crank  self-oiling  type,  and 
electric  motors  are  employed,  very  little  attention  need  be  paid 


COMMERCIAL  SYSTEMS  OF  REFRIGERATION      35 

to  lubrication,  and  the  item  of  attendance  becomes  very  small 
indeed. 

SEMI-AUTOMATIC  SYSTEMS 

THE  semi-automatic  system  usually  employed  to  meet  such 
conditions  is  illustrated  diagrammatically  in  Fig.  10.    It  will  be 


Fig.   10. — Semi- Automatic  Congealing  Tank  System 

noted  that  this  system  is  essentially  the  same  as  the  congealing- 
tank  system  illustrated  in  Fig.  9,  except  for  the  addition  of  an 
automatic  expansion  valve  V  and  some  suitable  safety  device  P  V 
for  preventing  the  occurrence  of  abnormal  pressures.  In  the  case 
of  other  than  electrical  power,  this  may  be  a  simple  mechanical 
device,  such  as  a  spring  or  a  weight-loaded  safety  valve  between 
the  high-pressure  and  the  low-pressure  sides  of  the  system.  In  the 
case  of  electric  power  a  device  actuated  by  pressure,  such  as  is 
shown  diagrammatically  in  Fig.  11,  may  be  employed.  Such  a 
device  consists  essentially  of  either  a  Bourdon  tube  or  a  diaphragm 
D  arranged  to  move  a  lever  arm  A  in  such  a  way  as  either  to  dis- 
engage a  latch  holding  a  spring-opening  electric  switch  closed  or, 
where  there  is  a  no-voltage  release  coil  in  the  motor-controlling 
circuit,  the  device  may  be  arranged  as  in  P  D,  Fig.  12.  Here  the 
diaphragm  D  bowing  outward  under  abnormal  pressure  P  is 
employed  simply  to  make  an  electric  contact  C  for  short-circuiting 
a  no-voltage  coil  which,  being  thereby  deenergized,  allows  a  spring 
to  open  the  motor  circuit  and  interrupt  the  operation  of  the  refrig- 
erating system,  just  as  would  occur  in  case  of  failure  of  line  voltage. 
It  is  almost  unnecessary  to  add  that  a  thermostat  T  may  be  simi- 
larly employed  to  stop  the  refrigerating  machine  when  the  desired 
temperature  has  been  produced  in  the  cold-storage  compartments. 


36    ELEMENTARY  MECHANICAL  REFRIGERATION 


I 


the  case  of  a  spring-opening  switch  an  outside  source  of 
such  as  a  storage  battery,  would  have  to  be  used  in  con- 
nection with  the  thermostat  to  supply  sufficient 
power  to  operate  the  latch.  Instead  of  a  laminated- 
blade  form  of  thermostat  controlling  a  battery 
circuit,  a  thermostatic  device  T  D,  Fig.  12,  worked 


Fig.    12.— Electrically   Actuated   Circuit 
Breaking  Device 


Fig.  11.— Pressure 
Actuated  Circuit 
Breaking  Device. 

by  the  expansion  force  of  a  gas  under  pressure  may  be  employed. 
In  this  case  a  small  amount  of  some  volatile  liquid,  such  as  anhy- 
drous ammonia,  is  placed  in  a  small  closed  receiver  Rf  and  con- 
nected to  the  thermostatic  device  T  D  by  a  small  tube.  Any  de- 
creased temperature  in  the  cold-storage  compartment  R  causes  a 
corresponding  decrease  in  pressure  in  the  receiver  R'  and  beneath 
the  diaphragm  df,  which  allows  it  to  return  to  its  normal  flat  posi- 
tion where  it  effects  the  making  of  an  electrical  contact  at  C'  which 
stops  the  machine. 

COMPLETELY  AUTOMATIC  SYSTEMS 

Still  more  elaborate  systems  have  been  devised  to  the  end  of 
eliminating  all  attendance.  " Completely  automatic"  systems 
divide  themselves  into  two  classes  according  to  the  two  possible 
cycles  of  cause  and  effect  on  which  the  systems  may  be  operated. 
In  the  first  system,  illustrated  diagrammatically  in  Fig.  13,  vari- 
ations in  temperature  in  the  cold-storage  room  R  effect  the  starting 
and  stopping  of  the  refrigerating  machine,  which  through  the  re- 
sulting variations  in  back  pressure  effects  the  regulation  of  the 
flow  of  refrigerant  to  the  expansion  coils  and  through  the  result- 
ing variations  in  head  pressure  effects  the  regulation  of  the  flow  of 
water  on  the  condenser  coils. 

In  the  second  system,  illustrated  diagrammatically  in  Fig.  14, 
variations  in  temperature  in  the  cold-storage  room  R,  instead  of 
effecting  the  starting  and  stopping  of  the  refrigerating  machine, 


COMMERCIAL  SYSTEMS  OF  REFRIGERATION      37 

and  indirectly  the  regulation  of  the  flow  of  the  refrigerating  me- 
dium, in  this  case  directly  controls  the  flow  of  the  refrigerant 
through  a  thermostatic-expansion  valve  V,  which  in  turn  controls 
the  starting  and  stopping  of  the  machine  through  the  resulting 
pressures.  The  cycle  of  operation  of  each  system  is  followed  out 

in  detail  below. 

THERMOSTAT  CONTROL 

The  thermostatically  controlled  system  shown  in  Fig.  13 
employs  a  laminated-blade  or  other  reliable  type  of  thermostat 
for  making  and  breaking  two  electric  circuits  which,  without  going 
into  full  detail  regarding  the  complete  circuit,  stops  and  starts 


Fig.  13. — Completely  Automatic  Refrigerating  System,  Tkermostatic  Control 

the  machine  through  the  operation  of  an  appropriate  automatic 
motor-controlling  panel  represented  diagrammatically  by  the 
electrical  solenoid  S,  which,  when  energized,  raises  the  motor- 
controller  arm  slowly  over  the  rheostat  segments.  The  dee'ner- 
gizing  of  this  solenoid  through  short-circuiting,  when  the  thermo- 
stat makes  the  circuit  through  the  stopping  contact,  allows  the 
rheostat  arm  to  drop,  open  circuiting  and  stopping  the  motor. 
The  operation  of  the  machine  is  to  draw  the  refrigerant  vapor 
from  the  expansion  coils  E  and  discharge  it  into  the  condenser  C, 
which  operation  reduces  the  pressure  in  the  former  and  increases 
the  pressure  in  the  latter  coils.  The  reduction  in  pressure  in  the 
expansion  or  low-pressure  side  of  the  system  allows  a  properly 
adjusted  spring  s  or  weight  on  the  expansion  valve  V  to  overcome 
the  back  pressure  of  the  gas  exerted  beneath  the  diaphragm  d, 
which  forces  the  attached  valve  stem  down,  opens  the  valve  and 
allows  the  refrigerant  to  flow  from  the  liquid  receiver  R  to  the 
expansion  coils.  In  a  similar  manner  the  increased  head  or  con- 
denser pressure  operating  on  a  water  controlling  valve  W  V, 
which  instead  of  closing  with  increasing  pressure,  opens  and  ad- 
mits ccoling  water  to  the  condenser  C. 


38    ELEMENTARY  MECHANICAL  REFRIGERATION 


The  evaporation  of  the  liquid  refrigerant  admitted  to  the 
expansion  coils  by  the  expansion  valve  produces  an  increase  in 
pressure  which  overcomes  the  pressure  of  the  spring  above  the 
diaphragm  and  closes  the  valve  until  the  pressure  is  so  reduced 
by  the  drawing  away  of  the  vapors  by  the  compressor  that  the 
spring  again  overcomes  the  pressure  of  the  gas  below  the  dia- 
phragm, when  the  valve  opens  and  more  liquid  is  allowed  to  pass. 
As  a  matter  of  fact,  there  is  no  appreciable  variation  in  back  pres- 
sure and  accordingly  no  intermittence  in  the  feed  of  the  liquid. 
The  valve  acts  simply  as  a  pressure-reducing  valve,  maintaining 
that  back  pressure  for  which  it  is  adjusted  until  the  machine  stops, 
when  the  evaporation  of  the  residual  liquid  in  the  expansion  coils 
produces  an  abnormal  rise  in  back  pressure  which  overcomes  the 
tension  of  the  spring  and  tightly  closes  the  valve. 

When  the  machine  is  stopped,  and  no  more  hot  high-pressure 
gas  is  discharged  into  the  condenser,  the  cooling  water  soon  reduces 
the  temperature  and  corresponding  pressure  in  the  high-pressure 
side  of  the  system,  which  allows  the  spring  in  the  water  valve  W  V 
to  overcome  this  reduced  pressure  and  close  the  valve,  interrupting 
the  flow  of  water  to  the  condenser. 

EXPANSION  VALVE  CONTROL 

In  the  second  method  of  control,  illustrated  in  Fig.  14,  an 
increase  in  temperature  causes  the  thermostatic  fluid  in  the  ther- 


0  II 

r 

R 

\ 

I 

Fig.  14. — Completely  Automatic  Refrigerating  System — Thermostatic 
Expansion  Valve  Control 

mostatic  tube  T  to  expand  and  exert  an  increased  pressure  under 
the  diaphragm  d  of  the  thermostatic  expansion  valve  V,  over- 
coming the  adjusting  spring  s,  opening  the  valve  and  admitting 
liquid  refrigerant  to  the  expansion  coils.  This  increase  in  expan- 
sion-coil pressure,  caused  by  the  introduction  of  the  liquid,  over- 
comes the  pressure  of  the  spring  above  the  diaphragm  of  the 


COMMERCIAL  SYSTEMS  OF  REFRIGERATION      39 

pressure-actuated,  motor-controlling  device  M  C  making  the 
electric  circuit  to  the  motor  and  starting  the  machine.  The  result- 
ing decrease  in  back  pressure  allows  the  spring  of  the  expansion 
valve  to  arrest  itself,  forcing  the  diaphragm  down  and  throttling 
the  incoming  liquid  to  the  requirements  of  the  compartment. 
When  the  temperature  has  been  sufficiently  reduced,  the  corre- 
spondingly reduced  pressure  in  the  thermostatic  tube  T  allows  the 
spring  s  to  close  the  thermostatic  expansion  valve  V  and  the 
reducing  pressure  in  the  expansion  coils  is  now  overcome  by  the 
spring  in  the  motor-controlling  device  M  C,  which,  operating 
in  the  opposite  direction  due  to  the  decreased  pressure,  stops  the 
motor. 

The  automatic  water  valve  shown  in  Fig.  14  operates  on  the 
same  principle  as  that  described  in  Fig.  13.  In  the  semi-automatic 
systems  illustrated  diagrammatically  in  Figs.  10  and  12,  as  well  as 
in  the  completely  automatic  systems,  Figs.  13  and  14,  electric 
power  is  employed. 

AUTOMATIC  CONTROL  OF  FEEDS  IN  PARALLEL 

The  automatic  systems  above  described  have  quite  serious 
limitations  because  of  the  arrangement  of  all  the  expansion  coils 
in  series,  a  condition  which  not  only  limits  the  ability  of  the 
system  to  accurately  maintain  the  various  temperatures  often 
required,  but  also  imposes  unusual  friction  to  the  passage  of  the 
refrigerating  fluid.  This  second  condition  makes  it  necessary 
to  operate  the  compressor  at  a  lower  back  pressure  than  would 
otherwise  be  necessary,  in  order  to  produce  the  desired  tempera- 
tures at  the  expansion  valve  end  of  the  expansion  coils. 

While  little  has  as  yet  been  accomplished  commercially,  a 
system  has  been  devised  and  patented  by  Stephen  C.  Wolcott 
for  the  automatic  control  of  systems  in  which  the  several  cold 
storage  compartments  are  each  provided  with  expansion  coils 
installed  in  parallel  and  each  fed  by  an  independent  liquid  press- 
ure reducing  valve,  controlled  by  the  temperatures  in  the  respect- 
ive compartments. 

In  the  Wolcott  system  the  motor  circuit  is  so  arranged  that 
the  compressor  will  continue  to  operate  so  long  as  the 
temperature  in  any  one  of  the  compartments  is  sufficiently 
high  to  keep  its  controlling  thermostat  on  the  operating  contact. 
As  the  temperatures  of  the  several  compartments  are  successively 


40    ELEMENTARY  MECHANICAL  REFRIGERATION 

reduced,  the  thermostats  make  low-temperature  contacts,  which, 
by  means  of  springs,  weights,  or  other  outside  agencies,  effect 
the  closing  of  stop  valves  placed  in  the  return  ends  of  the  expan- 
sion coils.  As  each  low-temperature  or  motor-stopping  contact 
is  made  by  the  thermostats,  the  corresponding  high-temperature 
or  motor-starting  contact,  arranged  in  parallel  for  the  control 
of  the  main  motor  circuit,  is  broken.  When  the  last  compartment 
has  been  sufficiently  cooled  and  the  last  of  the  parallel  controlling 
circuits  broken,  the  last  stop  valve  is  closed  and  the  machine 
is  made  to  suspend  operation  until  a  sufficient  rise  in  temperature 
in  some  one  of  the  compartments  causes  the  controlling  thermostat 
of  that  compartment  to  open  the  stop  valve  of  the  expansion  coil 
in  question,  and  at  the  same  time  to  actuate  the  controlling 
mechanism  to  start  the  motor. 

The  reduction  in  back  pressure  in  each  open  coil,  due  to  the 
operation  of  the  compressor,  causes  the  liquid  pressure  reducing 
valve,  controlling  the  feed  of  that  coil,  to  admit  refrigerant  as 
required  until  the  rise  in  back  pressure,  due  to  the  evaporation  of 
the  refrigerant  remaining  in  the  coil  when  the  thermostat  effects 
the  closing  of  the  stop  valve  on  the  end  of  the  coil,  again  closes  it. 

Among  the  numerous  types  of  small  refrigerating  machines 
designed  for  capacities  suitable  for  household  and  other  purposes 
where  only  a  few  hundred  pounds  of  cooling  effect  are  required 
per  twenty-four  hours,  the  following  are  the  most  interesting 
from  the  viewpoint  of  mechanical  construction,  one  being  an  ab- 
sorption and  the  other  a  compression  type  of  machine. 
A  SMALL  CAPACITY  ABSORPTION  MACHINE 

The  absorption  machine  described  below,  the  invention  of  Dr. 
J.  W.  Morris,  is  of  particular  interest  in  that  it  employs  water  as  a 
working  medium,  instead  of  ammonia,  and  caustic  potash  or  potas- 
sium hydrate  as  an  absorbing  medium  instead  of  water.  In  number 
and  functions  the  several  parts  of  the  Morris  machine  are  similar  to 
those  of  the  usual  absorption  machine  employing  ammonia  as  a  work- 
ing medium.  Their  construction,  however,  is  very  different,  since 
to  employ  water  as  a  medium  to  extract  heat  at  the  freezing  point  or 
below  requires  a  vacuum  of  29.75  inches  and  over.  Dr.  Morris's 
experimental  machine  employed  glass  tubes  in  the  place  of  iron 
pipes,  the  joints  being  made  by  means  of  short  pieces  of  rubber 
tubing  wound  with  thread  and  painted  to  ensure  air  tightness. 
The  machine  is  started  under  high  vacuum,  which  is  further 


COMMERCIAL  SYSTEMS  OF  REFRIGERATION     41 

increased  by  the  high  affinity  which  the  absorbing  medium  has 
for  water.  Under  the  high  vacuum  maintained  in  the  refrigerator, 
the  working  medium  (water)  boils  at  temperatures  of  32°  and  slight- 
ly lower,  depending  on  the  pressure,  sodium  chloride  or  salt 
being  dissolved  in  the  water  to  keep  it  from  freezing.  The  vapor 
or  " steam"  passes  from  the  refrigerator  to  the  absorber — where 
it  unites  with  the  concentrated  potassium  hydrate  (strong  liquor) 
to  form  dilute  potassium  hydrate  (weak  liquor),  which  is  pumped 
over  to  the  generator  (still).  Here  the  water  vapors  are  driven 
off  to  the  condenser,  after  which  the  resulting  strong  potassium 
hydrate  is  allowed  to  flow  back  to  the  absorber,  where  it  absorbs 
more  aqueous  vapor  coming  from  the  refrigerator  by  way  of  the 
condenser. 

The  still  is  heated   by  a   small  gas  flame  under  automatic 


r       Water  Vapor    ^^?\ 

u 

^> 

.  

/ 

! 

/ 

^-  — 
s~~ 

ivuxi                 water  vapor 

r 

Wa 

M 

^^ 

H20 

Cooler 
Water  and  Salt 

KOH 
Absorber 
Caustic  Soda 

H20f 
Still 
KOH 

H2O 

Condenser 

11 

y 

II     $ 
J  J     n  ««,* 

/ 

tter                Strong-  KOH             f  ^  4= 

<*««                                                                                                                            -^  «3S»                      _ 

Fig.  15. — Morris  Absorption  Machine 

control.  As  in  the  usual  type  of  absorption  machine,  the  weak 
liquor  flows  from  the  generator  to  the  absorber  because  of  the 
higher  pressure  in  the  former,  the  only  place  where  power  is 
necessary  being  where  the  strong  liquor  is  passed  from  the  absorber 
back  to  the  generator.  Here  a  " potassium  hydrate"  pump, 
paralleling  in  action  the  ammonia  pump  of  the  usual  system,  is 
required.  In  the  Morris  machine  this  pump  consists  of  a  little 
hydraulic  ram  actuated  by  the  pressure  of  the  cooling  water 
on  its  way  to  the  condenser. 

A  SMALL  CAPACITY  COMPRESSION  MACHINE 
The  compression  type  of  machine  designed  to  meet  the  require- 
ments of  the  small  consumer  of  refrigeration  seeks  to  overcome 
one  of  the  often  prohibitive  features  of  the  usual  types  when 
adapted  to  household  use,  viz.,  the  escaping  of  the  working  fluid 
through  packed  glands  and  gasket  joints,  by  enclosing  the  whole 
mechanism  in  a  hermetically  sealed  case.  The  machine  in  ques- 


42    ELEMENTARY  MECHANICAL  REFRIGERATION 

tion,  designed  and  patented  in  1895  by  a  Frenchman  named 
Marcel  Audiffren,  consists  essentially  of  two  small  gas  compressors 
suspended  on  a  shaft  which  runs  longitudinally  through  a  dumb- 
bell-shaped enclosing  casing.  This  shaft  is  provided  with  cranks 
in  line  with  the  compressor  cylinders  and  the  whole  is  so  arranged 
that  when  the  casing  and  shaft  are  revolved  and  the  compressor 
remains  stationary,  a  reciprocating  motion  is  given  to  the  com- 
pressor piston  as  in  the  usual  type.  The  casing,  mounted  on 
suitable  bearings,  with  its  axis  horizontal,  is  half  submerged  in 
a  tank  so  arranged  that  one  end  of  the  dumb-bell-shaped  casing 
revolves  in  a  liquid  on  one  side  of  a  partition  through  this  tank, 
while  the  other  part  containing  the  compressor  revolves  in  another 
liquid  on  the  other  side  of  the  partition.  Two  ducts  are  provided 
through  the  shaft  connecting  the  two  parts  of  the  casing,  one  of 
which  forms  a  suction  line  to  the  compressor  and  the  other  an 
expansion  or  liquid  line  to  the  other  chamber. 

When  charged  with  a  refrigerating  liquid,  the  tank  surrounding 
Casing  Casing 


Fig.  16. — Audiffren  Compression  Machine 

the  casing  containing  the  compressor  is  filled  with  cooling  water, 
that  surrounding  the  other  casing  with  brine,  and  the  machine 
placed  in  operation.  The  action  of  the  compressor  is  to  draw  the 
vaporized  gaseous  refrigerant  from  the  expansion  chamber,  com- 
press it,  and  discharge  it  into  its  condensing  chamber,  where,  being 
surrounded  by  cooling  water,  it  again  liquefies  under  the  higher 
pressure.  The  liquid  refrigerant,  thrown  to  that  part  of  the 
casing  most  remote  from  the  axis  of  rotation,  enters  the  liquid 
line  and  is  conducted  to  the  other  compartment,  where  evaporat- 
ing at  a  lower  pressure,  it  refrigerates  the  brine  surrounding  the 


COMMERCIAL  SYSTEMS  OF  REFRIGERATION       43 

refrigerator  chamber,  and  finally  returns  as  a  gas  to  the  compressor 
to  be  again  liquefied  by  the  cooling  water  surrounding  the  con- 
denser chamber. 

THE  SELECTION  OF  A  REFRIGERATING  SYSTEM 

While  local  conditions  must  be  the  deciding  factors  in  every 
case,  congealing-tank  systems  of  small  capacity  usually  compare 
quite  favorably  with  the  brine-circulation  systems  of  similar 
capacities;  but  it  must  be  remembered  that  both  systems  have 
the  disadvantage  of  being  inherently  inefficient  because  of  the 
necessity  of  operating  under  lower  back  pressures  in  order  to  pro- 
duce the  correspondingly  lower  temperatures  required  to  effect 
the  double-heat  transfer.  At  the  lower  pressures  fewer  pounds  of 
the  refrigerating  medium  are  passed  through  the  compressor  per 
revolution  and  a  greater  number  of  pounds  are  necessary  to  pro- 
duce a  given  refrigerating  effect,  each  of  which  conditions  makes 
it  necessary  to  speed  up  the  compressor  in  order  to  produce  the 
same  amount  of  cooling  duty. 

By  the  direct  expansion  of  the  refrigerant,  cold  is  produced 
just  where  it  is  required  and  more  nearly  at  the  temperatures 
required.  And  incidentally,  aside  from  the  saving  in  power  required 
to  operate  the  compressor  and  to  pump  the  brine,  a  saving  is  made 
in  investment  for  a  suitable  room  and  for  foundations  of  brine 
tanks  and  pumps,  as  well  as  for  the  tanks  and  pumps  themselves 
and  the  necessary  piping  and  insulation,  etc.  Thermal  losses  due 
to  radiation  through  the  insulation  of  these  members  and  through 
that  due  to  the  heating  effect  of  pumping  the  brine  are  entirely 
eliminated. 

Small  systems  may  be  satisfactorily  operated  semi-automatic- 
ally  at  the  expense  of  somewhat  more  attendance,  and  usually 
effect  a  considerable  saving  in  cost  of  power  by  the  substitution 
of  some  efficient  type  of  combustion  engine.  The  advisability 
of  such  a  substitution  at  the  present  day  of  an  unquestionably 
reliable  combustion  engine  depends  almost  entirely  on  the 
relative  local  cost  of  attendance,  and  the  cost  of  power  developed 
by  electricity,  illuminating  gas,  gasolene,  kerosene,  fuel  oil  or 
producer  gas. 

The  type  of  system  best  adapted  to  a  given  set  of  requirements 
can  be  determined  only  after  carefully  considering  the  relative 
importance  of  such  factors  as  cost  of  power,  cost  of  attendance, 
allowable  temperature  variation,  probable  earning  power  of  plant 
and  availability  of  capital. 


CHAPTER  IV 

A.   THE  COMPRESSION  SYSTEM 

WHILE  it  is  impossible  to  show  in  a  single  illustration  all  the 
details  entering  into  the  mechanical  construction  of  a  complete 
refrigerating  system,  the  diagrammatic  representation,  Fig.  17,  is 
more  complete  than  the  elementary  diagrams  already  shown,  and 


Fig.  17. — General  Arrangement  of  Compression  Refrigerating  System 

will  suffice  for  the  explanation  of  the  cycle  of  operation  of  the 
compression  system. 

EXPANSION  SIDE 

The  cycle  begins  with  liquid  anhydrous  ammonia  conducted 
to  the  expansion  coils  through  a  liquid  line  and  regulated  by  appro- 
priate expansion  valves.  The  source  of  the  liquid  ammonia  may  be 
either  a  liquid  receiver,  which,  as  already  shown,  is  one  of  the 
essential  members  of  the  system  in  practical  operation;  or  it  may 
be  an  ammonia  shipping-drum  from  which  ammonia  is  introduced 
into  the  system  by  the  process  of  charging.  In  either  case  the  first 
function  of  the  refrigerant  is  to  enter  the  expansion  coils  in  the 
compartment  to  be  refrigerated  and  there  to  evaporate  (boiling 
at  a  temperature  dependent  on  the  suction  or  "back  pressure" 


THE  COMPRESSION  SYSTEM  45 

within  the  coils)  and  absorb  heat  from  the  surrounding  objects. 
If  the  back  pressure  be  46  pounds  gauge,  or  less,  the  temperature 
of  the  boiling  liquid  will  be  32°  Fahrenheit,  the  freezing  point  of 
water,  or  below,  and  the  pipes  containing  the  refrigerating  medium 
at  these  temperatures  will  soon  be  covered  with  a  coating  of  frost. 
If,  on  the  other  hand,  the  back  pressure  in  the  coils  is  above  46 
pounds  gauge,  the  temperature  of  the  boiling  liquid  will  be  above 
32°  Fahrenheit,  and  no  frost  will  be  formed.  Refrigeration  will  be 
produced  whenever  the  temperature  of  the  expansion  coils  is  lower 
than  that  of  the  air  in  the  cooler,  regardless  of  whether  frost  is 
formed  or  not  and,  according  to  the  amount  of  atmospheric  humid- 
ity, uncongealed  moisture  may  or  may  not  be  precipitated  on  the 
pipes. 

Having  vaporized  in  the  expansion  coils,  the  ammonia  vapor 
enters  the  return  header  which  conveys  it  back  to  the  suction  side 
of  the  compressor.  This  return  line  is  usually  fitted  with  a  "scale 
trap"  constructed  similarly  to  a  simple  steam  separator.  The 
function  of  this  trap  is  to  prevent  any  scale  from  the  inside  of  the 
pipes,  or  other  foreign  substance,  from  entering  and  damaging  the 
compressor.  From  the  scale  trap  the  gas  passes  through  the  suc- 
tion valves  into  the  compressor. 

COMPRESSION  SIDE 

On  leaving  the  compressor  the  hot,  high-pressure  ammonia 
gas  passes  through  the  discharge  valves  and  out  into  the  two  legs 
of  the  main  discharge  pipe,  which  come  together  in  a  "T"  just 
below  the  large  hand-operated  discharge  valve  at  the  left-hand 
side  of  the  compressor  cylinder.  Leaving  the  discharge  valve,  the 
gas  passes  into  the  side  of  the  pressure-tank  head,  and  is  given  a 
spiral  motion  as  it  descends  into  the  tank.  The  centrifugal  force 
produced  by  this  spiral  motion  is  intended  to  aid  in  precipitating 
any  entrained  oil  which  the  gas  may  hold  in  suspension  against  the 
outside  of  the  tank.  The  gas  then  passes  up  through  the  hot  gas 
line,  through  a  " check  valve"  (sometimes  omitted)  located  a 
little  above  the  level  of  the  top  of  the  condenser,  and  down  into 
the  header  connecting  the  bottom  pipes  of  the  several  stands  of 
condensers.  The  loop  is  placed  in  the  hot-gas  line  to  prevent  con- 
densing liquid  from  running  back  down  into  the  pressure  tank 
when  the  compressor  is  shut  down. 

The  gas  entering  the  bottom  pipe  of  the  condenser  passes  up 
through  successive  pipes  while  the  water  distributed  over  the  top 


46    ELEMENTARY  MECHANICAL  REFRIGERATION 

pipe  trickles  down,  producing  the  desirable  counter-current  cooling 
effect,  in  which  the  hottest  water  encounters  the  hottest  gas  at 
the  bottom  and  the  coolest  water  the  coolest  gas  at  the  top  of  the 
condenser. 

As  fast  as  the  ammonia  is  condensed  in  the  pipes  of  the  con- 
denser it  is  conducted  away  through  smaller  liquid-drip  pipes  con- 
nected with  a  common  liquid  header.  The  outlet  from  this  header 
also  rises  to  form  a  short  " goose-neck"  which  is  intended  to  keep 
the  header  always  full  of  liquid  and  prevents  gas  from  being  drawn 
down  to  the  tank  through  the  liquid  line.  In  trying  to  ascend 
through  the  column  of  descending  liquid  in  a  small  liquid  line, 
bubbles  of  gas  offer  no  inconsiderable  resistance  to  the  passage  of 
the  liquid.  The  obvious  remedy  for  this  difficulty  is  the  installa- 
tion of  lines  of  liberal  diameter. 

If  the  gas  is  carried  down  into  the  liquid  tank  it  can  escape  by 
going  up  the  equalizer  line  into  the  top  of  the  condenser.  The 
ammonia  previously  liquefied  in  the  condenser  under  a  pressure 
of  from  135  to  200  pounds,  according  to  the  temperature  of  the 
cooling  water,  is  conveyed  first  to  the  receiver.  This  consists  of 
an  appropriate  cylindrical  containing  vessel  which  acts  as  a  storage 
tank  in  which  the  liquefied  ammonia  is  collected  and  from  which 
it  passes  as  required  into  the  expansion  coils.  The  flow  of  this 
high-pressure  liquid  into  the  expansion  coils  is  regulated  by  expan- 
sion valves,  which  are  virtually  nothing  more  than  convenient 
mechanical  devices  for  accurately  varying  the  opening  through 
which  the  liquid  ammonia  must  pass  on  its  way  to  the  expansion 
coils. 

REFRIGERATION  AVAILABLE  IN  EXPANSION 

As  stated,  the  word  " expansion"  has  been  erroneously 
applied  to  these  valves  and  coils,  because  of  the  idea,  also  erro- 
neous, that  the  liquid  ammonia  vaporizes  or  expands  immediately 
when  the  pressure  is  relieved  as  it  passes  the  regulating  valve 
and  enters  the  cooling  coils.  As  a  matter  of  fact,  before  it  is  pos- 
sible for  a  pound  of  ammonia  to  change  from  the  liquid  to  the 
gaseous  state,  it  must  be  supplied  with  about  573  B.t.u.  of  heat.* 

In  practice,  not  all  of  the  heat-absorbing  capacity,  or  negative 
heat,  of  a  pound  of  anhydrous  ammonia  available  at  0°  Fahren- 
heit can  be  utilized  for  useful  cooling  work,  on  account  of  the 
cooling  work  which  must  first  be  expended  on  the  ammonia 

*Evaporation  assumed  to  be  under  atmospheric  pressure. 


THE  COMPRESSION  SYSTEM  47 

itself  in  order  to  reduce  its  temperature  from  that  of  the  condenser 
to  that  of  the  cooler.  This  may  be  illustrated  by  a  similar  process 
in  which  water  is  the  medium.  The  amount  of  heat  that  must  be 
abstracted  from  one  pound  of  water  at  32°  Fahrenheit  in  order  to 
freeze  it  is  144  B.t.u.  On  this  basis,  a  ton  of  ice  would  represent 
288,000  B.t.u.  of  negative  heat.  In  practice,  the  expenditure  of 
this  amount  of  cooling  will  not  freeze  a  ton  of  water,  because  it 
must  first  be  reduced  from  its  natural  temperature,  or,  in  crystal- 
ice  systems,  from  the  temperature  of  the  distilled  water  tank  to 
32°  Fahrenheit.  This  involves  a  further  expenditure  of  one  nega- 
tive B.t.u.  per  pound  per  degree  cooled. 

If  the  573  B.t.u.  were  absorbed  at  the  expansion  valve,  which 
its  immediate  vaporization  assumes,  there  would  be  no  further 
heat-absorbing  capacity  in  the  ammonia,  and  its  introduction  into 
the  expansion  coils  would  be  useless. 

Besides  the  principal  pipe  circuit  just  described,  the  compressor 
is  provided  with  a  set  of  bypass  connections  for  reversing  its  oper- 
ation so  as  to  draw  the  ammonia  from  the  condenser  and  discharge 
it  into  the  expansion  coils,  as  well  as  other  so  called  " pump-out" 
lines  through  which  ammonia  may  be  pumped  out  of  other  parts 
of  the  system  in  case  it  becomes  necessary,  as  when  making 
repairs. 

DIRECT  EXPANSION  CYLINDER  COOLING 

In  Fig.  17  is  shown  a  small  liquid  line  running  from  the  liquid 
tank  to  the  compressor  cylinder.  This  line  is  provided  with  an  ex- 
pansion valve  through  which  ammonia  may  be  admitted  to  the 
compressor,  to  prevent  abnormal  heating  of  the  piston  and  pack- 
ing when  starting  up,  or  at  any  other  time  when  the  ammonia 
returning  to  the  compressor  is  not  sufficiently  cold  to  insure  satis- 
factory operating  of  the  compressor.  Another  small  pipe  line 
connects  the  lubricating  system  on  the  compressor  with  the  pres- 
sure tank.  Through  this  line  oil  passing  over  with  the  discharged 
ammonia  gas  and  separated  out  in  the  pressure  tank  may  be  blown 
back  into  the  lubricating  system.  On  entering  this  line  the  oil 
passes  first  through  a  small  strainer  which  intercepts  any  scale 
or  foreign  substances  that  might  otherwise  return  to  the  compressor 
and  cut  the  valves  or  cylinder  walls. 

Details  of  construction  of  the  various  parts  of  a  compression 
system  are  too  numerous  to  warrant  an  attempt  to  fully  describe 
them  here.  Since  the  ammonia  compressor  is  so  important  a  mem- 


48    ELEMENTARY  MECHANICAL  REFRIGERATION 

her  of  the  refrigerating  system,  however,  a  brief  description  setting 
forth  its  several  characteristics  will  be  in  order. 

TYPES  OF  AMMONIA  COMPRESSORS 

Ammonia  compressors  are  divided  into  two  principal  classes, 
double-acting  and  single-acting.  The  former  type  is  most  com- 
monly horizontal,  although  frequently  of  vertical  construction. 
The  single-acting  type  is  almost  exclusively  a  vertical  machine. 
Each  type  has  its  own  followers  among  builders,  and  under  certain 
conditions  possesses  some  advantages  over  the  other.  While  there 
is  much  variation  in  details  of  design  among  the  various  builders, 


Fig.  18. — Vertical  Single-acting  Ammonia  Compressor — Section  and 
Typical  Elevation. 

the  accompanying  illustrations,  Figs.  18  and  19,  are  the  most 
characteristic  of  the  general  types.  Fig.  20  shows  a  modification 
of  the  vertical  single-acting  machine  which  may  be  said  to  be 
typical  of  the  compressor  of  small  capacity. 

VERTICAL  SINGLE-ACTING  COMPRESSORS 
The  accompanying  illustration,  Fig.  18,  giving  a  lateral  ele- 
vation in  section  of  a  characteristic  vertical  single-acting  ammonia 


THE  COMPRESSION  SYSTEM  49 

compressor,  shows  the  relative  arrangement  of  compressor  and 
engine  cylinders  as  well  as  the  principal  details  of  design.  In  this 
type  of  compressor  the  vaporized  refrigerant  enters  the  compressor 
near  the  bottom,  passes  up  through  the  suction  valve,  located  in 
the  compressor  piston,  during  the  downstroke,  and  is  compressed 
and  discharged  through  the  discharge  valve,  located  in  the  safety 
head,  during  the  upstroke  of  the  piston.  The  compressor  may  be 
water  jacketed  or  not.  Popular  preference,  however,  is  in  favor  of 
the  water  jacket,  and  most  machines  are  so  built. 

Vertical  compressors  possess  the  advantage  of  requiring  less 
floor  space  than  horizontal  machines  and  the  disadvantage  of 
being  less  accessible  for  repairs.  The  inaccessibility  of  suction 
valves  located  in  compressor  pistons  is  offset  by  the  unmistakable 
advantage  offered  by  this  type  of  machine  in  that  these  suction 
valves  can  be  made  of  generous  area,  and  the  inertia  of  the  valve 
tends  ,to  hasten  its  closing  promptly  as  the  piston  reverses  its 
direction  of  travel  at  the  lower  end  of  its  stroke.  This  largely 
prevents  gas  from  escaping  from  the  cylinder  during  the  time  re- 
quired for  the  acting  of  the  ordinary  stationary  valves  unless  they 
be  heavily  spring  loaded,  a  condition  which  tends  to  prevent  the 
back  pressure  in  the  cylinder  from  quite  reaching  the  height  of  that 
in  the  suction  line  from  the  coolers.  Inertia  also  tends  to  open  the 
valve  immediately  as  soon  as  the  piston  begins  its  downward 
stroke,  giving  full  opportunity  for  the  cylinder  to  fill.  The  spring 
below  the  suction  valve  should  be  of  such  strength  as  to  almost 
balance  the  weight  of  the  valve,  so  that  the  inertia  of  the  valve 
may  act  promptly  at  each  end  of  the  stroke. 

Vertical  single-acting  compressors  are  usually  provided  with  a 
" safety  head"  which  is  normally  held  securely  to  its  seat  by  strong 
springs,  but  which,  in  the  event  of  abnormal  quantities  of  liquid 
ammonia  or  broken  parts  entering  the  cylinder  above  the  piston, 
is  pushed  back,  compressing  the  springs  and  thereby  saving  the 
machine  from  the  strains  that  would  otherwise  occur.  One  of  the 
principal  advantages  claimed  by  the  advocates  of  the  single-acting 
compressor  is  that  the  use  of  the  safety  head  allows  the  compressor 
pistons  to  be  operated  with  less  clearance  than  would  be  practicable 
in  the  case  of  double-acting  machines,  a  condition  which  insures  a 
more  complete  expulsion  of  the  gas. 


50    ELEMENTARY  MECHANICAL  REFRIGERATION 

THE  HORIZONTAL  DOUBLE-ACTING  MACHINE 

Fig.  19  represents  a  horizontal  half  section  of  a  characteristic 
horizontal  double-acting  ammonia  compressor.  The  right-hand 
portion  of  the  cut  shows  the  exterior  of  the  head  end  of  the  com- 
pressor-cylinder valve  housings,  suction  and  discharge  connections 
and  valves.  The  remaining  portion  of  the  cut  shows  the  details 
of  construction  of  the  compressor  cylinder,  water  jacket,  piston, 


Fig  19. — Horizontal  Double-acting  Ammonia  Compressor — Section  and 
Typical  Elevation. 

suction  and  discharge  valves,  double  stuffing  box  and  means  of 
lubricating  the  piston  rod.  The  outer  wall  of  the  water  jacket  is 
formed  by  the  main  frame  casting,  which  is  bored  and  fitted  with  a 
working  cylinder  liner,  consisting  of  a  straight  sleeve  forced  into 
place  by  hydraulic  pressure  and  bored  to  the  required  size.  The 
valves  in  this  type  of  compressor  are  arranged  radially  to  the  hemi- 
spherical cylinder  heads.  The  piston  rod  is  provided  with  a  pri- 
mary stuffing  box  where  it  enters  the  compression  cylinder.  The 
packing  in  this  box  is  tightened  by  a  primary  packing  nut  which 
carries  a  long  sleeve,  the  other  end  of  which  is  provided  with  a 


THE  COMPRESSION  SYSTEM 


51 


secondary  stuffing  box  and  packing  nut.  The  main  stuffing  box, 
containing  the  bulk  of  the  packing,  withstands  the  high  pressure 
of  the  ammonia  in  the  compressor  cylinder.  The  small  stuffing 
box  at  the  end  of  the  sleeve  is  provided  with  sufficient  packing  to 


Discharge  Discharge 

Pipe  Pipe 

Discharge 

Suction   LSDrxJ3,Valve" 
Valve 


Crank 
Case  H 


Main 
Bearing 


Fig.  20- — Enclosed  Crank  Case  Ammonia  Compressor — Elevation  in  Section 

withstand  the  pressure  of  the  oil  circulated  by  the  oil  pump  through 
the  hollow  sleeve  surrounding  the  piston  rod,  in  order  to  insure 
constant  lubrication  of  and  to  maintain  an  oil  seal  on  the  main 
stuffing  box. 

The  general  appearance  of  the  horizontal  double-acting  com- 
pressor just  described  is  shown  in  the  longitudinal  elevation, 
just  above  the  sectional  view  of  the  compressor  cylinder. 
INCLOSED  CRANK-CASE  COMPRESSORS 

In  addition  to  the  two  principal  types  of  compressors  previous- 
ly described,  the  inclosed-crank  type  is  deserving  of  mention  be- 


52    ELEMENTARY  MECHANICAL  REFRIGERATION 

cause  of  the  great  number  of  such  machine?  of  small  capacity  now 
being  installed.  Details  of  design  of  this  type  of  compressor  are 
even  more  varied  than  those  of  the  machines  already  described, 
and  it  is  difficult  to  point  out  a  single  design  that  can  be  said  to 
be  more  characteristic  of  the  type  than  another. 

In  the  illustration,  Fig.  20,  the  refrigerant  vapor  enters  the 
compressor  cylinders  through  suction  valves  located  in  the  cylinder 
head.  Valves  so  located  cannot  be  made  of  so  liberal  dimensions 
as  those  located  in  the  compressor  piston,  and  the  assistance  which 
inertia  offers  in  the  way  of  opening  and  closing  suction  valves 
located  in  the  piston  cannot  be  realized.  To  offset  this  disadvan- 
tage, oil  from  the  crank  case  is  much  less  likely  to  be  carried  over 
into  the  condenser  and  low-pressure  side  of  the  system. 

Machines  of  the  inclosed  type  are  especially  adapted  to  use 
where  little,  or  only  inefficient,  attendance  is  available.  Less 
attention  is  possible  in  this  type  of  machine,  principally  because 
of  the  design  of  the  stuffing  box  and  the  main-bearing  lubri- 
cation. The  crank  case  being  filled  with  oil  to  the  center 
of  the  crank  shaft,  and  the  outboard  bearing  being  usually  ring 
oiling  or  provided  with  a  compression  grease  cup,  little  attention 
to  lubrication  is  necessary.  There  are  no  reciprocating  piston 
rods  to  pack,  the  only  stuffing  box  required  being  on  the  crank 
shaft,  where  it  is  always  well  lubricated  and  not  subject  to  such 
extremes  of  temperature  as  are  the  pistons  in  other  types  of  ma- 
chines. This  type  of  compressor  is  peculiarly  well  adapted  for 
use  in  connection  with  automatic  systems. 

B.    THE  ABSORPTION  REFRIGERATING  SYSTEM 

IT  has  already  been  pointed  out  under  the  subject  of  "The 
Development  of  Mechanical  Refrigeration"  that,  while  Carre 
invented  the  absorption  machine,  the  way  was  paved  by  the  earlier 
experiments  of  Faraday,  who  discovered  that  silver  chloride  pos- 
sessed the  property  of  absorbing  ammonia.  Faraday  is  said  to 
have  experimented  with  silver  chloride  saturated  with  ammonia 
in  a  closed  glass  tube,  one  end  of  which  was  immersed  in  a  freezing 
mixture  of  ice  and  salt,  while  the  other  end  was  heated.  The 
ammonia  gas  driven  off  from  the  silver  chloride  in  the  hot  end  of 
the  tube  was  liquefied  in  the  cold  end  of  the  tube  under  the  pres- 
sure generated  by  the  heat.  See  Fig.  21. 

Faraday  discovered  that  if  he  reversed  the  tube  so  that  the 


THE  ABSORPTION  SYSTEM 


53 


end  containing  the  silver  chloride  from  which  the  ammonia  had 
been  driven  off  was  immersed  in  the  freezing  mixture,  the  liquefied 


Silver  Chloride 

and  Absorbed 

Ammonia 


Fig.  21. — Faraday's  Elementary  Absorption  Machine 

ammonia  in  the  other  end  of  the  tube  would  boil,  producing  a 
remarkably  low  temperature.  The  cold  vaporized  ammonia  was 
absorbed  by  the  silver  chloride,  so  that  if  the  tube  were  occasion- 
ally reversed  the  device  would  be  made  to  traverse  the  cycle  of  an 
elementary,  intermittent  absorption  machine.* 

A  modern  commercial  absorption  machine  consists  primarily 
of  five  parts,  three  of  which  are  also  present  in  the  compression 
machine.  This  is  shown  in  Fig.  22,  which  is  a  diagrammatic  rep- 
resentation of  an  elementary  absorption  and  compression  machine 
having  their  condensers  and  complete  expansion  sides  in  common. 

In  the  compression  system  it  has  been  shown  how  the  low- 
pressure  cold  gas  returning  from  the  expansion  coils  enters  the 
suction  end  of  the  compressor  cylinder,  and  how,  after  it  has  been 
transferred  to  the  compression  end  of  the  cylinder,  it  is  compressed 
and  passed  over  into  the  condenser.  Reference  to  the  figure  will 
ghow  that  in  the  absorption  machine  the  compressor  cylinder  is 
replaced  by  an  absorber,  a  liquid  pump  and  a  generator.  In  the 
absorption  system  the  gas,  returning  from  the  expansion  coils, 
enters  the  absorber  (corresponding  to  the  suction  end  of  the  com- 
pressor), is  transferred  to  the  generator  (corresponding  to  the  dis- 
charge end  of  the  compressor)  by  a  pump,  through  the  valves  of 
which  it  passes  just  as  it  flows  through  the  valves  of  the  compressor 
piston. 

In  the  absorption  plant  the  ammonia  (liquor)  pump  can  be 
made  much  smaller  than  the  compressor  gas  pump  used  in  the 
compression  system,  because  the  actual  work  of  compressing  the 

*This  experiment  of  Faraday's  is  described  more  in  detail  by  Mr. 
Gardner  T.  Voorhees  in  "  Ice  and  Refrigeration,"  October,  1908. 


54    ELEMENTARY  MECHANICAL  REFRIGERATION 


ammonia  gas  to  the  point  at  which  it  can  be  liquefied  by  the  cooling 
water  in  the  condenser  is  performed  by  the  direct  heat  of  steam 
rather  than  by  the  heat  generated  by  the  expenditure  of  energy 
behind  the  compressor  piston.  To  facilitate  the  use  of  steam  for 
this  purpose,  the  cold  ammonia  gas  returning  from  the  expansion 
coils  is  absorbed  or  dissolved  in  water  in  the  absorber,  and  the  re- 
sulting strong  aqua  ammonia,  known  as  "strong  liquor,"  is  pumped 
into  the  generator  or  ammonia  boiler,  where  it  is  heated  by  a  series 
of  steam  coils  which  drive  off  the  gaseous  ammonia  at  a  high  pres- 
sure, just  as  water  vapor  or  steam  is  driven  off  under  high  pressure 
in  a  steam  boiler. 


Discharge 
End  — 

Ammonia 


Compressor 


Fig.  22. — Elementary  Compression  and  Absorption  Machine  with  Common 
Condensing   and  Expansion  Units 

The  high-pressure  ammonia  gas  driven  off  in  the  generator  of 
an  absorption  plant,  like  that  discharged  from  the  compressor  of  a 
compression  plant,  is  conducted  to  the  condenser,  at  which  point 
that  part  of  the  refrigerating  cycle  common  to  both  systems  begins. 

The  driving  off  of  the  ammonia  vapor  in  the  generator  changes 
the  strong  liquor  to  "weak  liquor,"  which,  being  under  a  higher 
pressure  than  the  liquid  in  the  absorber,  readily  flows  back  to  the 
absorber.  To  adapt  the  elementary  absorption  machine  just  de- 
scribed to  the  requirements  of  economical  commercial  apparatus, 
a  number  of  refinements  must  be  added.  Fig.  23  is  a  diagrammatic 
representation  of  a  modern  absorption  machine  of  well-known 
make. 

On  account  of  the  similarity  of  the  expansion  side  of  the  ab- 
sorption system  to  that  of  the  compression  system  already  de- 


56    ELEMENTARY  MECHANICAL  REFRIGERATION 

scribed  in  detail,  it  will  be  necessary  to  trace  the  working  medium 
through  only  that  part  of  the  cycle  between  the  expansion  coils 
and  the  condenser. 

COOLER 

In  the  type  of  machine  illustrated  in  Fig.  23,  the  expansion 
side  consists  of  a  brine  cooler  of  the  vertical  cylindrical  or  shell 
type,  such  as  is  most  commonly  used  in  connection  with  absorption 
machines,  but  to  some  considerable  extent  with  compression 
machines  as  well.  The  brine,  usually  calcium  chloride,  is  circu- 
lated through  nests  of  spiral  coils  within  the  cylindrical  shell  of 
the  cooler,  and  the  anhydrous  ammonia  is  expanded  into  the  space 
between  the  coils  and  the  shell.  The  amount  of  liquid  present  is 
readily  observed  by  means  of  a  gauge  glass.  The  cold  ammonia 
vapor  leaving  the  top  of  the  cooler  passes  through  the  gas-suction 
line  to  the  absorber,  where  it  is  joined  by  the  weak  liquor  which 
has  just  undergone  cooling  in  the  "  double-pipe "  weak-liquor 
cooler.  Since  the  absorption  of  the  ammonia  gas  into  the  weak 
liquor  takes  place  with  the  evolution  of  a  considerable  amount  of 
heat,  further  means  for  cooling  the  liquor  must  also  be  provided 
in  the  absorber. 

ABSORBER 

In  some  cases  the  absorber  is  of  the  double-pipe  type,  similar 
to  double-type  condensers  and  brine  coolers.  The  type  here  illus- 
trated consists  of  a  horizontal  cylinder  containing  coils  of  pipe 
through  which  the  cooling  water  which  has  previously  done  duty 
in  the  ammonia  condenser  passes.  The  cold,  weak  liquor  is  ad- 
mitted at  the  top  of  the  cylinder,  passes  down  among  the  cooling 
coils,  and  there  mingles  with  and  absorbs  the  cold  ammonia  gas 
from  the  brine  cooler. 

As  the  cooling  water  has  already  been  heated  through  several 
degrees  in  passing  through  the  pipes  of  the  ammonia  condenser, 
it  is  expedient  that  a  counter-current  cooling  effect  be  carried 
out,  in  which  the  warmer,  outgoing  cooling  water  cools  the 
weaker  aqua  ammonia,  and  the  incoming  cooler  water  is  employed 
to  reduce  the  temperature  of  the  strong  aqua  ammonia  on  its  way 
to  the  generator  through  the  ammonia  pump  and  exchanger. 

EXCHANGER 

The  exchanger  is  a  horizontal  steel  shell  capable  of  carrying 
the  full  generator  pressure  through  which  the  comparatively  cool 


THE  ABSORPTION  SYSTEM  57 

strong  liquor  is  pumped  on  its  way  from  the  bottom  of  the  ab- 
sorber to  the  bottom  of  the  generator.  This  rich  liquor  is  shown 
entering  the  shell  of  the  exchanger  at  the  right-hand  side,  after 
which  it  traverses  a  spiral  pipe  coil  and  finally  passes  out  into  the 
top  of  the  analyzer,  shown  just  above  the  generator.  The  ex- 
changer is  provided  with  nests  of  pipe  coils  connected  in  parallel, 
through  which  passes  the  hot  weak  aqua  ammonia,  supplied  to  the 
manifold  at  the  top  of  the  exchanger  by  a  pipe  running  from  the  bot- 
tom of  the  generator.  In  the  countercurrent  flow,  the  hot  weak 
liquor  which  must  eventually  be  cooled  in  descending  through  the 
pipes  gives  up  a  part  of  its  heat  to  the  cooler  rich  liquor  which 
must  eventually  be  heated  when  ascending  around  the  coils.  By 
this  heat  exchange,  cooling  water  is  economized  in  the  absorber 
and  steam  in  the  generator. 

ANALYZER 

Leaving  the  top  of  the  exchanger  shell,  the  cool  rich  liquor 
passes  to  the  top  of  the  analyzer.  Here  it  is  allowed  to  trickle  down 
over  a  set  of  metal  trays,  where,  coming  in  contact  with  the  am- 
monia vapors  rising  from  the  generator,  the  countercurrent  heat- 
exchanging  effect  is  still  further  continued.  The  hot  ammonia 
vapor,  entraining  more  or  less  aqueous  vapor  as  it  rises  from  the 
surface  of  the  liquid  in  the  generator,  in  passing  up  through  the 
analyzer  on  its  way  to  the  condenser  encounters  the  descending 
rain  of  cool  rich  liquor  on  its  way  to  the  generator.  The  former, 
which  must  eventually  be  liquefied  in  the  condenser,  is  cooled, 
and  the  latter,  which  must  eventually  be  boiled  in  the  generator, 
is  heated.  This  advantageous  heat  interchange  also  has  the  effect 
of  actually  condensing  and  returning  to  the  generator  a  large  per- 
centage of  the  entrained  aqueous  vapors  passing  off  with  the  am- 
monia, and  also  of  liberating  some  ammonia  gas  through  the  heating 
of  the  gas-saturated  rich  liquor.  Where  ample  analyzer  capacities 
are  employed,  the  incoming  rich  liquor  should  be  within  a  very  few 
degrees  of  the  evaporating  temperature  by  the  time  it  finally  reaches 
the  surface  of  the  boiling  liquid. 

GENERATOR 

The  generator,  or  "still,"  as  it  is  frequently  called,  is  the  am- 
monia boiler  for  the  evaporation  of  the  weak  liquor  enriched  and 
changed  into  strong  liquor  by  the  absorption  of  ammonia  gas 


58    ELEMENTARY  MECHANICAL  REFRIGERATION 

direct  from  the  expansion  coils  in  the  absorber.  It  consists  of  a 
substantial  steel  shell  provided  with  a  heavy  cast-iron  head 
through  which  pass  the  ends  of  the  steam  coils  supplying  the  heat 
required  for  driving  off  the  ammonia.  The  strong  aqua  ammonia 
enters  at  the  top,  where  it  remains  by  virtue  of  its  specific  gravity 
being  lower  than  that  of  the  weaker  liquor  at  the  bottom  of  the 
generator.  The  water  of  condensation  from  the  steam  used  in  the 
generator  is  usually  returned  to  the  boilers.  This  can  be  effected 
either  by  an  automatically  controlled  pump,  or  by  a  suitable  high- 
pressure  trap. 

RECTIFIER 

After  leaving  the  analyzer,  the  hot  ammonia  gas  passes  to  the 
rectifier,  a  water-cooled  coil  of  pipes  of  sufficient  area  to  insure  the 
condensation  of  any  aqueous  vapors  that  may  have  escaped  con- 
densation in  the  analyzer.  The  liquid  condensed  in  the  rectifier 
is  rich,  saturated  liquor  which  is  returned  to  the  generator  by  way 
of  the  analyzer. 

CONDENSER 

From  the  rectifier  the  ammonia  gas,  which  should  now  be  prac- 
tically free  from  aqueous  vapors,  is  passed  to  the  condenser.  Con- 
densers for  absorption  machines,  like  those  for  compression  ma- 
chines, may  be  of  either  the  atmospheric  double-pipe  or  shell  type 
as  preferred.  The  anhydrous  ammonia  liquefied  in  the  condenser 
passes  to  an  anhydrous  receiver,  similar  to  those  used  in  the  com- 
pression system,  from  which  it  is  drawn  as  required  for  expansion 
in  the  brine  cooler,  its  flow  through  the  feed  line  being  regulated 
by  the  usual  expansion  valve.  After  evaporation  in  the  brine 
cooler  the  ammonia  gas  again  passes  to  the  absorber,  after  which 
the  working  cycle  is  repeated. 

CYCLE  TRAVERSED  BY  AMMONIA 

This  can  be  readily  traced  by  following  the  course  of  the  heavy 
arrows  in  Fig.  23.  The  circuits  of  both  the  gaseous  and  the  aqueous 
components  of  the  aqua-ammonia  refrigerant,  as  well  as  that  of 
the  cooling  water,  can  be  more  readily  followed  out  by  means  of 
the  diagram,  Fig.  23,  in  which  all  mechanical  details  have  been 
omitted.  The  several  members  of  the  refrigerating  system  illus- 
trated in  Fig.  23  are  represented  by  shaded  areas  occupying  ap- 
proximately the  same  relative  positions  on  the  diagram.  The  path 
of  the  ammonia  is  represented  by  a  heavy  solid  line;  that  of  the 


THE  ABSORPTION  SYSTEM 


59 


water  component  of  the  aqua-ammonia  refrigerant  by  a  narrow 
solid  line;  and  that  of  the  cooling  water  by  a  broken  line.  The 
direction  of  travel  in  each  case  is  indicated  by  arrows. 

Cooking  _Water 


»eak  Liquor 


Cooling  Water 


Strong  Liquor 

Fig    24. — Diagrammatic  Representation  of  an  Absorption 
Refrigerating  System 

From  this  diagram,  as  well  as  from  Fig.  23,  it  will  be  seen  that, 
as  "  anhydrous  ammonia,"  the  refrigerant  starting  from  the 
" anhydrous  receiver"  passes  to  the  " brine  cooler,"  where  in 
changing  to  the  gaseous  state  it  performs  its  sole  function  of  ab- 
sorbing heat  from  the  brine.  As  saturated  low-temperature  am- 
monia vapor,  the  refrigerant  starting  from  the  brine  cooler  passes 
to  the  absorber,  where  it  enters  into  solution  or  is  absorbed  by  the 
weak  liquor  from  the  generator,  forming  strong  liquor.  As  hot 
strong  liquor  the  refrigerant  starting  from  the  absorber  passes 
through  the  exchanger,  where  it  gives  up  some  of  its  heat  to  the 
weak  liquor  on  its  way  to  the  absorber,  then  on  by  way  of  the 
analyzer  into  the  generator,  where  the  ammonia  gas  is  driven  out 
of  the  strong  liquor  solution,  under  high  pressure,  by  the  appli- 
cation of  heat,  and  passes  through  the  analyzer  and  rectifier  into 
the  condenser,  leaving  the  impoverished  aqua  ammonia  or  weak 
liquor  behind  in  the  generator. 

In  the  condenser,  the  heat  originally  absorbed  by  the  anhy- 
drous ammonia  in  changing  from  the  liquid  to  the  gaseous  state  in 


60    ELEMENTARY  MECHANICAL  REFRIGERATION 

the  brine  cooler,  as  well  as  that  added  to  increase  its  temperature 
and  drive  it  out  of  solution  in  the  generator,  is  given  up  to  the  cool- 
ing water,  circulated  through  the  condenser,  causing  the  ammonia 
to  return  to  the  liquid  state,  after  which  it  flows  to  the  anhydrous 
receiver,  and  the  cycle  is  again  traversed. 

The  aqueous  component  of  the  aqua-ammonia  refrigerant, 
starting  from  the  bottom  of  the  absorber  in  company  with  the 
ammonia  in  the  form  of  strong  liquor,  passes  through  the  exchanger 
and  analyzer  into  the  generator.  Here  it  is  separated  from  the 
greater  part  of  the  ammonia  and  returns  through  the  exchanger 
and  weak-liquor  cooler  to  the  absorber.  Here  it  again  joins  the 
anhydrous  ammonia,  forming  strong  liquor,  and  retraces  the  path 
just  described. 

PATH  OF  COOLING  WATER 

The  cooling  water  is  admitted  first  to  the  ammonia  condenser, 
where  it  performs  its  most  important  function  of  removing  heat 
from  and  liquefying  the  ammonia  gas.  After  leaving  the  ammonia 
condenser  it  is  still  cool  enough  to  be  capable  of  absorbing  a  con- 
siderable amount  of  heat  from  the  strong  liquor  in  the  absorber, 
more  from  the  weak  liquor  fresh  from  the  generator  in  the  weak- 
liquor  cooler,  and  still  more  from  the  hot  ammonia  gas  fresh  from 
the  generator  in  the  rectifier,  after  which  it  usually  passes  to  waste. 

Still  another  line  might  have  been  drawn  on  the  diagram  in  Fig. 
24,  indicating  the  path  traversed  by  the  heat  from  the  point  of  its 
absorption  from  the  brine  in  the  brine  cooler  to  that  of  its  expul- 
sion with  the  cooling  water  from  the  condenser.  Such  a  line,  how- 
ever, would  coincide  with  that  representing  the  ammonia  from  the 
point  where  the  heat  and  the  vapors  of  the  refrigerant  leave  the 
brine  cooler,  continuing  to  the  condenser,  where  it  would  cross 
over  and  join,  that  representing  the  cooling  water.  It  would  then 
follow  this  line  through  its  circuitous  passage  to  the  point  where, 
together  with  the  water,  the  heat  flows  away  to  the  sewer. 

COUNTER  CURRENT  EFFECT 

It  should  be  noted  that  throughout  the  entire  system  a  coun- 
ter-current effect  is  carried  out  between  the  cooling  and  the  cooled 
substances.  In  the  absorber  the  direction  of  travel  of  the  cooling 
water  is  upward  through  the  cooling  coils,  while  that  of  the  cooled 
strong  liquor  is  downward  around  the  outside  of  the  cooling  coils. 
In  the  exchanger,  the  hot  weak  liquor  from  the  generator  passes 


THE  ABSORPTION  SYSTEM  61 

in  one  direction  through  a  nest  of  pipe  coils,  while  the  somewhat 
cooler  strong  liquor  from  the  absorber  flows  in  the  opposite  direc- 
tion around  the  outside  of  the  cooling  coils.  In  the  double-pipe 
weak-liquor  cooler,  the  cooling  water,  after  passing  through  the 
cooling  coils  of  the  absorber,  passes  in  one  direction  through  the 
inner  pipes,  while  the  hot  weak  liquor  passes  in  the  opposite  direc- 
tion between  the  inner  and  the  outer  pipes.  In  the  analyzer  the 
hot  ammonia  gas  passes  upward'  through  a  rain  of  cooler  strong 
liquor.  Likewise,  in  the  double-pipe  condenser  a  similar  counter- 
current  effect  is  produced. 

By  these  counter-current  cooling  effects,  in  which  the  coldest 
cooled  substance  gives  up  its  heat  to  the  coldest  cooling  substance, 
and  the  hottest  cooled  substance  to  the  warmest  cooling  substance, 
the  outgoing  substance  is  cooled  more  nearly  to  the  temperature 
of  the  incoming  cooling  substance  than  wrould  otherwise  be  possi- 
ble, thus  effecting  economy  not  only  in  the  amount  of  the  cooling 
substance  required  but  also  in  the  operation  of  the  system  through 
the  reduction  in  the  amount  of  the  refrigerating  medium  required 
for  a  given  amount  of  cooling  effect. 


CHAPTER  V 
SIMPLE  COMPARISONS 

I.    ELEMENTARY  COMPRESSION  AND  ABSORPTION  REFRIGERATING 

SYSTEMS 

THE  fundamental  natural  laws  on  which  artificial  refrigeration 
depends  can  be  readily  understood  by  comparing  their  action  with 
better  known  processes.  The  flow  of  heat  from  a  higher  to  a  lower 
thermal  level,  the  operation  upon  which  mechanical  refrigeration 
depends,  is  clearly  illustrated  by  the  flow  of  water  from  a  higher 
to  a  lower  level.  Heat  can  no  more  be  made  to  flow  up  hill  than 
can  water.  By  the  use  of  appropriate  mechanical  devices,  both 
heat  and  water  can  be  raised  from  lower  to  higher  planes.  When 
water  is  raised  to  a  given  hight,  its  ability  to  do  work,  or  its 
energy,  is  proportionately  increased.  When  heat  is  raised  to  a 
higher  thermal  level  its  ability  to  do  work,  or  its  energy,  is  also 
proportionately  increased. 

PUMP  FOR  RAISING  WATER 

A  simple  machine  for  the  performance  of  work  on  a  gas  usually 
takes  the  form  of  a  pump  similar  to  that  used  for  pumping  liquids. 
Such  a  machine  is  represented  diagrammatically  in  Fig.  25.  This 
machine  is  so  constructed  that  successive  strokes  of  the  piston 
will  effect  the  raising  of  the  liquid  from  tank  1  to  tank  2.  To  pre- 
pare for  the  comparison  which  is  to  be  drawn  later,  let  the  cylinder 
be  supposed  to  be  filled  with  sponges,  which  will  not  materially 
affect  the  operation  of  the  machine.  In  this  case  foot-pounds  of 
work  are  delivered  through  the  piston  for  the  purpose  of  raising  the 
water  from  a  lower  to  a  higher  level  and  thereby  increasing  its  po- 
tential energy.  To  speak  more  practically,  it  transfers  the  liquid 
from  a  place  where  it  is  not  wanted  to  some  other  place  where  it  is. 

PUMP  FOR  RAISING  TEMPERATURE 

Only  slight  modifications  are  necessary  in  this  mechanism  to 
make  it  an  appropriate  machine  for  illustrating  the  principle  of 
the  compression  system  as  used  in  the  most  modern  processes  of 
mechanical  refrigeration.  A  refrigerating  machine  is  then  a  device 


SIMPLE  COMPARISONS 


63 


for  removing  heat  from  a  place  where  it  is  not  wanted  to  some  other 
place  where  it  can  be  conveniently  disposed  of.  Fig.  26  shows 
a  machine  similar  in  construction  to  that  shown  in  Fig.  25,  but 
instead  of  having  an  inlet  and  an  outlet  for  the  passage  of  a  liquid, 
its  cylinder  walls  are  constructed  of  a  very  thin  sheet  of  metal 
which  readily  allows  the  passage  of  heat  whenever  a  difference  in 
temperature  exists  between  the  substance  inside  and  that  outside 
of  its  walls. 

This  cylinder  employs  as  a  working  medium  ammonia  gas 
instead  of  sponges.    In  this  analogy  the  action  of  ammonia,  or  in 


Fig.    25- — Conventionalized    Diagram   of 
Pump  for  Raising  Water 

fact  any  refrigerating  medium,  in  absorbing  heat,  is  compared  to 
that  of  the  sponges  in  absorbing  water.  After  the  first  charge  of 
heat  has  been  squeezed  out  of  the  ammonia  and  that  of  water  out 
of  the  sponges,  both  the  ammonia  and  the  sponges  still  possess 
their  original  capacity  for  absorbing  more.  Both  the  heat  and  the 
water  are  drawn  in  or  absorbed  only  because  of  the  outside  in- 
fluence exerted  by  the  ammonia  and  the  sponges. 

Instead  of  two  tanks  at  different  levels  representing  difference 
in  " head"  or  potential  energy,  in  Fig.  26  there  are  two  tanks,  a 
and  6,  on  the  same  level,  but  containing  liquids  of  different  tem- 
peratures and  representing  difference  in  thermal  energy.  In  study- 
ing the  operation  of  the  elementary  refrigerating  engine  repre- 
sented in  Fig.  26,  it  must  be  assumed  that  the  cylinder  is,  to  be 


64    ELEMENTARY  MECHANICAL  REFRIGERATION 

filled  with  ammonia  gas  at  a  temperature  t\,  and  a  pressure 
pi,  the  piston  occupying  that  position  in  its  path  farthest  from 
X.  If  the  crankshaft  be  turned  through  one-half  of  a  revolution 
the  piston  will  arrive  at  X.  The  volume  of  the  gas  having  become 
greatly  diminished,  its  temperature  and  its  pressure  will  have 
been,  proportionately  increased  to  tz  p%*. 

At  the  end  of  stroke  the  piston  is  allowed  to  stop  and  by 
means  of  the  three-way  cock  C,  a  spray  of  water  is  allowed  to 


Fig.  26. — Conventionalized  Diagram  of  Compressor  for  liaising  Temperature 

flow  over  the  end  of  the  cylinder  in  which  the  hot  gas  is  confined, 
absorbing  a  portion  of  the  heat  of  compression,  and  consequently 
reducing  its  temperature  and  pressure  to  fa  p$.  The  machine  is 
now  made  to  complete  its  revolution  and  the  gas,  by  expanding 
with  the  increasing  cylinder  volume,  cools  itself  to  the  conditions 
of  U  p±.  At  the  other  end  of  the  stroke  the  piston  is  again  allowed 
to  stop,  and  by  reversing  the  three-way  cock  a  spray  of  water  is 
allowed  to  flow  over  that  portion  of  the  cylinder  through  which  the 

*  The  ratio  of  pressure  to  volume  in  the  case  of  adiabatic  compression  for 

p        y  1-3 
ammonia  is  expressed  by  the  equation  p-  =  yTTs'  which  means  that  the 

pressure  will  vary  inversely  in  the  1.3  power  of  the  volume. 


SIMPLE  COMPARISONS  65 

piston  has  just  passed.  The  gas  within  having  now  become  colder 
than  the  water,  because  of  having  expanded  after  reaching  the 
temperature  of  the  water,  again  absorbs  heat  from  it  as  it  passes 
in  a  thin  sheet  over  the  comparatively  large  surface  of  the  cylin- 
der, and  its  temperature  and  pressure  are  raised  to  their  original 
conditions  of  t\  pi,  after  which  the  cycle  is  again  traversed. 

WORKING    MEDIUMS 

In  this  example  the  ammonia  gas  within  the  cylinder  may  be 
compared  to  the  sponges  in  the  preceding  case.  During  the  ex- 
pansion the  gas  absorbs  heat  and  the  sponges  water.  During 
compression  both  the  heat  and  the  water  are  expelled  and  directed 
into  "  places  where  they  can  be  used,  or  conveniently  disposed 
of."  In  the  operation  of  the  mechanism  represented  in  Fig.  26, 
heat  is  taken  away  from  a  part  of  the  water  passed  over  the  cylinder 
and  given  to  the  other  part.  The  former,  or  "  refrigerated  "  water, 
being  conducted  into  tank  b,  and  the  latter,  which  contains  a 
double  share  of  heat,  into  tank  a. 

In  order  to  more  closely  approach  the  mechanism  employed  in 
practical  refrigeration  systems,  it  will  be  possible,  without  in  the 
least  altering  the  principles  involved,  to  slightly  modify  the  sys- 
tem represented  in  Fig.  26.  In  practice  the  operation  of  the  com- 
pressor must  be  continuous  and  the  cylinder  proper  would  have 
far  too  little  surface  to  allow  of  its  being  used  either  as  a  gas  cooler 
or  a  gas  heater,  as  was  done  in  the  foregoing  example. 

COMPRESSOR  AND  EXPANSION  ENGINE 

Let  it  be  assumed,  as  shown  in  Fig.  27,  that  a  portion  of  the 
cylinder  at  the  top  and  at  the  bottom  be  drawn  out,  forming  a 
cooling  or  condensing  coil  B  and  a  heating  or  expansion  coil  D  and 
at  some  convenient  point,  E,  the  passage  between  the  two  be 
contracted  to  a  sufficiently  small  cross  section  to  maintain  a  higher 
pressure  in  the  condenser  coil  than  in  the  expansion  coil,  the  com- 
pressor being  in  operation.  If  the  two  coils  be  sprinkled  with 
water,  or,  to  conform  more  closely  to  practice,  if  the  lower  coil  be 
entirely  submerged,  we  will  have  practically  the  same  conditions 
as  those  in  the  foregoing  example.  Starting  with  the  piston  in  the 
position  shown  in  Fig.  26,  the  cylinder  full  of  gas  is  under  conditions 
of  temperature  and  pressure  ti  pi.  By  compression  these  condi- 
tions are  changed  to  tz  pz,  which  the  cooling  of  the  spray  of  water 


66    ELEMENTARY  MECHANICAL  REFRIGERATION 

over  the  condenser  coil  tends  to  reduce  to  tsps.    In  the  compound 
machine,  Fig.  28,  ammonia  gas,  or  whatever  the  working  medium 


Water 
Supply 


Expansion  Coil 
Fig.  27. — Conventionalized  Diagram  of  Compression  Refrigerating  System 

maybe,  is  compressed  in  the  compression  cylinder  A,  after  which 
it  passes  to  the  condenser  B,  where  it  is  relieved  of  a  large  part  of  its 


Brine  Tank 


Fig.   28. — Conventionalized    Diagram    Showing   Compression    Cylinder   for 
Raising  and  Expansion   Cylinder  for  Lowering  Temperature 


SIMPLE  COMPARISONS  67 

heat.  From  the  condenser  the  gas  passes  to  the  expansion  cylinder 
C,  where  it  loses  more  heat  because  of  the  work  it  does  in  expanding 
behind  the  moving  piston.  This  work  done  by  the  gas  expanding 
behind  the  moving  piston  in  C,  (which  is  an  exact  equivalent  of  the 
amount  of  thermal  energy  lost,)  is  recovered,  since  it  assists  in 
compressing  the  gas  in  cylinder  A. 

REFRIGERATION  BY  CHANGE  OF  TEMPERATION  OF  GASES 

The  production  of  refrigeration  by  the  method  just  described 
depends  on  the  change  in  temperature  of  the  working  medium,  and 
not  on  its  liquefaction.  Machines  of  this  type  are,  accordingly, 
not  limited  in  choice  of  working  medium  to  those  which  are  easily 
liquefiable,  and  air  rather  than  ammonia  is  most  commonly  em- 
ployed. Such  machines,  known  as  cold  air  machines,  have  been 
used  extensively  in  the  past  on  shipboard,  their  favor  there  being 
due  to  the  dangers,  real  and  imaginary,  incident  to  the  use  of 
ammonia  and  other  liquefiable  refrigerants. 

Refrigeration  is  produced  by  cold  air  machines  by  the 
process  just  outlined.  The  air  is  first  compressed,  raising  its 
temperature,  and  allowed  to  do  work  in  expanding  behind  the 
piston  of  an  air  engine,  just  as  steam  is  allowed  to  do  work  by 
expanding  behind  the  piston  of  a  steam  engine.  The  air,  as  well 
as  the  steam,  is  cooled,  because  of  the  heat  converted  into 
mechanical  work.  The  exhaust  air  escaping  from  the  cylinder  of 
the  air  engine  into  the  atmosphere  of  the  cold-storage  room  is  often 
as  low  as  from  —50°  to  —85°  Fahrenheit  while  exhaust  steam, 
though  similarly  cooled  by  the  performance  of  work  in  the  steam 
cylinder,  usually  escapes  to  the  atmosphere  at  a  temperature  of 
212°  Fahrenheit  and  upward. 

In  practice  the  expanded  air  from  a  cold-air  refrigerating  ma- 
chine is  returned  to  the  compressor  and  used  over  and  over  again, 
as  this  reduces  the  losses  in  efficiency  due  to  the  presence  of  atmos- 
pheric moisture.  The  production  of  cold  by  the  expansion  of 
compressed  and  cooled  air  is  often  apparent  in  the  operation  of 
pneumatic  machinery  in  cold  weather,  in  which  case  the  tempera- 
ture of  the  exhaust  is  often  low  enough  to  freeze  the  aqueous  vapor, 
making  it  necessary  to  take  precautionary  measures  to  prevent 
the  closing  up  of  exhaust  outlets  by  the  accumulation  of  ice.  In 
practical  refrigerating  systems,  in  which  the  working  medium 
is  carried  through  the  liquid  state  in  order  to  make  use  of  the 


68    ELEMENTARY  MECHANICAL  REFRIGERATION 

latent  heat  of  liquefaction,  the  expansion  cylinder  is  omitted  as  in 
Fig.  27. 

In  the  example  cited  in  connection  with  Fig.  26  the  available 
refrigeration  is  obtained  by  simply  raising  and  lowering  the  tem- 
perature of  the  ammonia  gas,  of  which,  since  one  degree  of  sensible 
heat  represents  only  one-half  a  British  thermal  unit,  288  pounds 
would  have  to  be  lowered  one  degree  in  order  to  produce  an  effect 
equivalent  to  the  melting  of  one  pound  of  ice.  This  would  necessi- 
tate handling  tremendous  volumes  of  gas  to  produce  compara- 
tively small  results  of  refrigeration.  The  specific  heat  of  air  being 
only  about  one-half  that  of  ammonia  vapor,  approximately  twice 
as  many  pounds  of  the  former  as  of  the  latter  refrigerant  would 
have  to  be  employed  to  produce  a  given  cooling  effect.  At  atmos- 
pheric pressure  the  latent  heat  of  vaporization  for  ammonia  is  573 
and  the  specific  heat  of  the  liquid  is  unity,  while  that  of  the  gas 
at  constant  pressure  is  only  about  .5080.  Comparing  these  last 
values,  we  naturally  look  for  means  of  producing  refrigeration 
through  the  aid  of  the  latent  heat  of  vaporization  because  of  the 
great  heat  absorbing  capacity  of  this  process.  The  gas,  instead 
of  expanding  behind  a  piston,  is  allowed  to  escape  through 
a  restricted  opening,  E,  Fig.  27,  into  the  expansion  coil  below, 
in  which  a  considerably  lower  back  pressure  is  maintained 
through  the  efforts  of  the  compressor  which  is  constantly  drawing 
gas  from  the  lower  coil  and  discharging  it  into  the  upper 
coil.  In  passing  the  point  E,  the  conditions  of  temperature  and 
pressure  of  gas  drop  to  U  p*,  which  the  heating  effect  of  the  liquid 
surrounding  the  expansion  coil  finally  restores  to  ti  pi,  at  which 
point  it  meets  with  a  repetition  of  the  cycle.  The  utilization  of 
the  latent  heat  of  liquefaction  requires  no  mechanical  alterations 
in  the  system,  and  this  elementary  mechanism  illustrated  in 
Fig.  27,  when  put  in  operation  with  a  proper  charge  of  anhydrous 
ammonia  and  cooling  water  for  the  condensers,  is  capable  of  pro- 
ducing commercial  results  of  artificial  refrigeration. 

An  elementary  absorption  machine,  corresponding  to  the  com- 
pression machine  illustrated  in  Fig.  27,  is  shown  in  Fig.  29.  As  is 
pointed  out  in  another  chapter,  the  absorber  of  the  absorption 
machine  performs  the  function  of  the  suction  stroke  of  the  com- 
pressor in  the  compression  system,  and  -the  generator  that  of  the 
compression  stroke.  The  remaining  portion  of  the  cycle,  including 


SIMPLE  COMPARISONS 


69 


expansion  at  E,  and  evaporation  in  the  expansion  coil  also  remains 
as  in  the  compression  system. 


Water 
Supply 


Expansion  Coil  Absorber 

Fig.    29. — Conventionalized  Diagram  of  Absorption  Refrigerating  System 

II.  SIMPLE    COMPARISONS 
WATER  AND  AMMONIA  SYSTEMS 

It  has  already  been  shown  that  the  amount  of  heat  required 
to  raise  the  temperature  of  either  a  solid,  a  liquid  or  a  gas  through 
one  degree  is  very  small  compared  to  that  required  to  effect  a 
change  either  from  the  solid  to  the  liquid  or  from  the  liquid  to  the 
gaseous  state. 

In  the  case  of  anhydrous  ammonia,  for  example,  the  specific 

TABLE  i. 

COMPARATIVE  PROPERTIES  OF  WATER  AND  ANHYDROUS  AMMONIA 

Steam  and  Ammonia  Gas  NHa 

Temperature  of  decomposition 900 . 

Critical  Temperature 266. 

Specific  heat.     Constant  pressure 5080 

Specific  heat.    Constant  temperature 3911 

Latent  heat  of  evaporation.      Atmospheric  pressure 573 . 

Weight  per  cubic  foot  at  atmospheric  pressure 055 

Water  and  Ammonia  Liquid 

Temperature  of  evaporation.    Atmospheric  pressure — 28 . 5 

Specific  heat  of  the  liquid 1  to  1.23 

Latent  heat  of  fusion ( ) 

Weight  per  cubic  foot  at  32°  F 42.02 

Ice  and  Ammonia  Solid 

Temperature  of  fusion.      Atmospheric  pressure — 115. 

Specific  heat  of  the  solid ( ) 


HaO 
4500. 
698. 
.480 
.346 
966.1 
.0376 

212. 
1. 

144. 
62.42 


32. 
.5 

57.50 


Weight  per  cubic  foot  at  32° 


70    ELEMENTARY  MECHANICAL  REFRIGERATION 

heat  of  the  liquid  is  about  unity,  that  of  the  gas  about  .51  under 
constant  pressure  and  about  .39  at  constant  volume,  while  the 
latent  heat  of  evaporation  under  atmospheric  pressure  is  about 
573  B.t.u.  For  comparison  of  these  characteristics  with  similar 
ones  for  water  see  Table  I. 

It  has  also  been  shown  that  refrigeration  or  cooling  is  always 
effected  by  drawing  heat  out  of  one  substance  into  some  other 
substance  at  a  lower  temperature.  In  this  case  the  former  sub- 
stance is  refrigerated  and  the  latter  heated.  In  fact  refrigeration 
and  heating  are  two  different  views  of  the  same  operation. 

Refrigeration  and  heating  may  take  place  at  any  temperature. 
Metals,  for  example,  are  melted  in  a  furnace.  To  effect  the  change 
from  the  solid  to  the  liquid  state  considerable  amounts  or  heat 
have  to  be  supplied  to  satisfy  the  latent  heats  of  fusion,  and  we 
may  state  just  as  accurately  that  the  melting  metals  refrigerate 
the  furnaces  as  we  can  that  melting  ice  refrigerates  a  refrigerator. 

If  the  average  temperature  of  our  terrestrial  atmosphere  were 
a  few  hundred  degrees  higher  on  the  thermometric  scale,  we  might 
actually  employ  the  latent  heat  of  fusion  of  lead,  tin  or  other 
metals  as  we  now  employ  ice,  i.e.,  as  a  convenient  vehicle  for 
absorbing  and  carrying  away  comparatively  large  quantities  of 
heat.  With  the  low  temperatures  that  we  can  now  produce  we 
might  at  the  present  time  actually  employ  congealed  mercury  in 
our  refrigerators  in  the  place  of  ice  were  there  any  advantage  to  be 
gained  in  producing  cold  by  the  fusion  of  a  metal.  Any  substance 
might  be  used  for  absorbing  heat  for  the  purpose  of  cooling  other 
substances.  The  limits  of  temperature  between  which  practical 
use  of  refrigeration  can  be  made  are  so  narrow,  however,  that  the 
latent  heat  of  fusion  of  only  a  very  few  substances  can  be  employed 
and,  as  a  matter  of  fact,  only  that  of  one  substance,  ice,  is  em- 
ployed. Similarly  the  latent  heat  of  evaporation  of  only  a  com- 
paratively few  substances  falls  within  that  range,  and  since,  unfor- 
tunately, none  of  these  can  be  employed  because  of  other  reasons, 
only  the  specific  heats  of  available  natural  cooling  media,  which 
as  has  already  been  shown  afford  only  limited  heat  absorbing 
capacities,  can  be  employed. 

NATURAL  COOLING  MEDIUMS 

Even  the  so-called  refrigerating  mediums  such  as  ammonia, 
carbon  dioxide,  etc.,  which  substances  are  liquefiable  at  such  tern- 


SIMPLE  COMPARISONS  71 

peratures  as  to  make  their  respective  latent  heats  of  evaporation 
readily  available  for  the  production  of  artificial  cold,  must  in  turn 
be  cooled  by  some  natural  cooling  medium  after  they  have  ab- 
sorbed their  fill  of  heat  in  the  cold-storage  compartment.  As  will 
now  be  shown  the  most  commonly  employed  natural  cooling  me- 
dium is  water.  As  there  are  no  mediums  having  their  boiling  points 
so  located  as  to  make  their  latent  heats  of  evaporation  available  for 
cooling  the  primary  refrigerants  such  as  ammonia,  carbon  dioxide, 
etc.,  we  must  of  necessity  employ  the  more  limited  heat  absorbing 
capacities  available  in  the  specific  heat  of  some  convenient  natural 
cooling  medium.  These  heat  absorbing  capacities  available  in 
changes  of  temperature  without  change  of  state  are  so  very  lim- 
ited that  only  the  most  inexpen  ive  substances  such  as  air  and  water 
can  be  considered  for  cooling  on  the  large  scale  necessary  in  the 
case  of  steam  and  ammonia  condensers.  As  a  matter  of  fact,  these 
two  agents  are  practically  the  only  mediums  we  have  that  can 
be  employed  as  primary  cooling  agents 

Air  is  everywhere  available,  but  often  at  a  prohibitively  high 
temperature.  It  has  the  further  disadvantage  that  its  specific 
heat  is  very  small,  being  only  .2377.  Since  its  weight  is  only  .0706 
per  cubic  foot  the  prohibitive  volume  of  59.5  cubic  feet  would 
have  to  be  employed  to  absorb  a  single  B.t.u.,  this  assuming  a  rise 
of  one  degree  in  the  temperature  of  the  air,  or  16,136,000  cubic  feet 
to  carry  off  288,000  B.t.u.,  or  an  amount  equivalent  to  the  negative 
heat  of  one  ton  of  refrigeration.  Water  is  more  expensive  than  air, 
but  its  specific  heat  being  1.0  and  its  weight  being  62.5  pounds  per 
cubic  foot,  only  0.016  cubic  feet  is  required  to  absorb  one  B.t.u. 
Assuming  a  rise  in  temperature  of  one  degree,  4,608  cubic  feet 
will  carry  away  288,000  B.t.u.,  or  an  amount  equivalent  to  the 
negative  heat  of  a  ton  of  refrigeration.  Water,  after  all,  is  the 
natural  refrigerating  medium,  the  comparatively  small  specific 
heat  of  which  we  are  able  to  employ  only  because  of  the  cheapness 
of  the  medium. 

Where  the  price  of  water  is  abnormally  high  the  still  cheaper 
medium  air  is  employed  to  cool  it,  in  which  case  air,  with  its  ex- 
tremely small  specific  heat,  becomes  the  cooling  medium  into 
which  the  animal  heat,  solar  heat  and  heat  of  fermentation, 
removed  by  mechanical  refrigeration  from  cold-storage  houses  and 
breweries,  finally  gravitates.  The  temperature  of  the  boiling-point 
and  also  the  latent  heat  of  evaporation  of  water  is  unfortunately 


72    ELEMENTARY  MECHANICAL  REFRIGERATION 

too  high,  at  the  usual  working  pressures,  to  enable  us  to  use 
water  as  a  direct  refrigerant;  otherwise  this  medium  would 
undoubtedly  be  employed  in  the  place  of  the  several  mediums  now 
used.*  The  so-called  refrigerating  mediums  are  employed  only 
because  it  is  difficult  for  water,  when  used  as  a  refrigerant,  to 
reach  down  low  enough  to  get  hold  of  heat  at  cold  storage  tem- 
perature levels.  These  so-called  refrigerating  mediums  are  accord- 
ingly employed  to  splice  out  water  which  is  the  real  arm  of 
every  form  of  heat  dredge. 

HEATING  AND  REFRIGERATING  SYSTEMS 

The  striking  similarities  between  a  steam  and  a  refrigerating 
system,  together  with  the  fact  that  almost  everyone  is  more  or 
less  familiar  with  the  principles  involved  in  a  steam  boiler  and 
engine  plant,  makes  such  a  system  most  happily  convenient  for 
illustrating  the  principles  of  operation  of  a  direct  expansion  refrig- 
erating system. 

Except  that  the  cycle  of  operations  is  reversed,  a  steam  system 
consisting  of  a  boiler,  an  engine,  a  surface  condenser  and  means 
of  returning  the  condensation  from  the  condenser  to  the  boiler,  is 
mechanically  and  thermodynamically  an  almost  exact  counter- 
part of  a  refrigerating  system  consisting  of  expansion  coils,  a 
compressor,  a  surface  condenser,  and  means  of  returning  the  con- 
densation from  the  condenser  to  the  expansion  coils.  Theoretically 
ammonia  might  be  employed  as  a  working  medium  in  the  steam 
system  for  the  production  of  power,  and  water  might  be  employed 
as  a  working  medium  in  a  refrigerating  system  for  producing  refrig- 
eration. As  commercially  operated  the  prohibitive  disadvantages 
of  so  employing  the  working  mediums  are  too  apparent  to  warrant 

comment. 

EVAPORATING  AND  CONDENSING  MEMBERS 

In  these  two  similar  systems  a  shell  boiler  has  its  counterpart 
in  coolers  of  the  shell  type  and  a  water  tube  boiler  in  direct  expan- 
sion coils.  Each  is  a  receptacle  for  the  evaporation  of  its  respective 
working  medium,  the  evaporation  being  accomplished  in  the  for- 

*  As  a  matter  of  fact,  as  can  readily  be  seen  from  tables  of  properties  of 
saturated  steam,  water  can  be  employed  as  a  working  medium  for  producing 
refrigeration  when  not  too  low  temperatures  are  required.  The  impractica- 
bility of  operating  an  ordinary  compression  system  employing  this  medium 
is  evident  from  the  fact  that  to  cause  water  to  boil  at  a  temperature  even  as 
low  as  32°  Fahrenheit  requires  a  vacuum  of  29.74  inches  of  mercury. 


SIMPLE  COMPARISONS 


73 


mer  case  by  the  absorption  of  heat  liberated  in  the  combustion 
of  coal  in  the  fire-box,  and  in  the  latter  by  animal  or  solar  heat 
with  which  the  liquid  comes  in  contact  in  its  journey  through  the 
expansion  coils  immersed  in  comparatively  hot  brine  or  atmos- 
phere of  a  cold-storage  compartment.  The  system  just  described 
is  represented  diagrammatically  in  Fig.  31.  Corresponding  parts 
of  a  similarly  constructed  refrigerating  system  are  shown  in  Fig.  30. 

REFRIGERATING  FURNACE  GASES  AND  COLD  STORAGE  AIR 
In  the  former  case  heat  gravitates  from  the  furnace  gases  to 


Ammonia  Condenser  C 
Heat  given_.C  ~" 

up  here      "'  1 


Radiator  or  Steam  Condenser  R 


Expansion 
Valve 


)  Heat  Absorbed 
<r^~—  here 

Expansion 
)  Coil 


Heat  given 
up  here 


Trap 

-EH 


Heat 

Absorbed 

here 


Boiler 


Fig.    30- — Refrigerating   System 


Fig.   31. — Heating  System 


Diagrams  Showing   Similarity  of   Evaporating   and   Condensing   Units   of 
Heating  and  Refrigerating  Systems 

the  water  in  the  boiler  because  it  is  at  a  lower  temperature.  The 
water  is  heated  by  the  flow  and  the  furnace  is  refrigerated.  The 
steam  generated,  we  will  assume,  passes  to  a  steam  radiator  where 
heat  gravitates  from  it  to  the  cooler  surrounding  air.  By  this 
flow  the  air  is  heated  and  the  radiator  is  refrigerated.  If  the  sur- 
rounding air  were  hotter  than  the  radiator,  it  is  evident  that  the 
heat  flow  would  be  in  the  direction  of  the  outside  air  to  the  radiator. 
In  the  latter  case  heat  gravitates  from  the  comparatively  hot  air 
of  the  cold-storage  compartment  to  the  ammonia  in  the  expansion 
coils  because  the  ammonia  is  at  a  lower  temperature.  The 
ammonia  is  heated  and  the  air  is  refrigerated.  The  ammonia 
vapor,  we  will  assume,  then  passes  to  the  ammonia  condenser, 
where,  under  the  same  relative  conditions  as  existed  in  the  steam 
heating  system,  namely  of  the  surrounding  air  being  colder 
than  the  vapors,  it  would  lose  its  heat  and  condense.  As  the 
temperature  of  the  outside  air  or  even  any  available  cooling 
water  is  far  above  that  of  ammonia  vapors  returning  from  the 
expansion  coils,  a  condition  similar  to  that  of  the  hot  radiator  in 


74    ELEMENTARY  MECHANICAL  REFRIGERATION 

a  still  hotter  room  exists,  and  the  heat  flow  will  be  in  the  direction 
of  the  ammonia  and  no  condensation  can  take  place. 

CONDENSATION  OF  STEAM  AND  AMMONIA 

So  far,  the  difference  in  the  two  systems  is  that,  whereas  in  the 
case  of  the  steam  system,  the  vapors  are  hotter  than  they  need  be 
in  order  to  be  condensed  by  the  air  in  the  warm  room ;  in  the  case 
of  the  refrigerating  system,  the  ammonia  is  not  hot  enough  to  be 
condensed  at  the  temperature  of  the  atmosphere  or  any  avail- 
able condensing  water.  The  ammonia  vapors,  as  well  as  the 
steam,  must  be  condensed,  however,  before  they  can  be  made  to 
absorb  more  heat  in  the  expansion  coils  and  the  boiler,  respectively; 


Condenser  C 


Radiator  R 


Fig.  32. — Diagram  Showing  the  Combination  of  Similar  Parts  of  a  Heating 
and  a  Refrigerating  System  with  a  Steam  Driven  Compressor  to  Form 
a  Compression  Refrigerating  System 

but  as  the  steam  is  already  hotter  than  need  be  it  may  be  robbed 
of  a  part  of  its  heat  by  making  it  do  work  by  expanding  in  the 
cylinder  of  a  steam  engine.  Since  the  ammonia  vapor  is  too  cold 
to  be  condensed  by  any  available  cooling  medium  its  temperature 
must  be  raised.  This  is  accomplished  by  doing  work  on  it,  a  con- 
venient method  of  which  is  to  pass  it  through  an  ammonia  com- 
pressor. Since  there  is  too  much  heat  on  the  steam  side  and  not 
enough  on  the  ammonia  side,  the  two  systems  may  be  connected 
together  in  such  a  way  that  the  power  developed  by  the  steam  is 
exerted  on  the  ammonia.  Mechanically  this  is  effected  by  means 
of  a  direct-acting  steam-driven  ammonia  compressor,  illustrated 
diagrammatically  in  Fig.  32. 

In  the  absorption  system,  instead  of  converting  heat  into 
power  on  the  steam  side  of  the  system  and  the  power  into  heat  on 
the  ammonia  side  of  the  system,  a  more  direct  heat  interchange 
between  the  two  sides  of  the  system  is  effected  by  bringing  the 


SIMPLE  COMPARISONS  75 

steam  and  ammonia  into  close  proximity  in  a  generator,  repre- 
sented diagrammatically  by  the  two  overlapping  coils  substituted 
in  Fig.  33  for  the  compressor-driven  engine  in  Fig.  32. 

Ammonia  Condenser  C 


C 

t 

hT,                            > 

Generator 

C 

V  -J~ 

d         Boiler        D 

^) 

I^^=^JI 

c                              L 

r 

3  Expansion  Coil 

I                          N 

i^^^l 

Fig.  33. — Diagram  Showing  the  Combination  of  Similar  Parts  of  a  Heating 
and  a  Refrigerating  System  with  a  Generator  to  Form  an  Absorption 
Refrigerating  System 

III.    SIMPLE  COMPARISONS 
THE  REFRIGERATING  MACHINE  AS  A  "HEAT  PUMP" 

In  the  language  of  the  preceding  chapter,  the  functions  of  water 
pumps  and  heat  pumps  are  to  remove  water  and  heat,  respectively, 
from  places  where  they  are  not  wanted  to  some  other  place  where 
they  can  be  used  or  more  conveniently  disposed  of.  The  rudi- 
mentary mechanical  systems  by  which  this  is  effected  have  been 
explained.  The  object  of  the  present  chapter  is  to  continue  the 
analogy  between  the  flow  of  water  and  that  of  heat,  making  a 
somewhat  more  practicable  concrete  application  of  the  principles 
involved. 

Fig.  34,  waiving  the  question  of  obvious  inaccuracy  in  details, 
may  be  taken  to  represent  a  sectional  view  of  brewery  cellars 
located  on  the  bank  of  a  river.  The  floor  of  the  lower  cellar  is 
sufficiently  high  above  the  river  at  low  water  to  allow  the  water 
from  the  floors  to  drain  out  of  a  catch-basin  sunk  in  the  floor. 
This  condition  may  be  assumed  to  prevail  in  the  winter,  at  which 
time  it  is  also  possible,  on  account  of  the  low  temperature  of  the 
outside  atmosphere,  to  open  the  windows  and  let  the  heat  of  fer- 
mentation "  drain "  out.  Cold  being  a  condition  resulting  from 
the  absence  of  heat,  just  as  dryness  is  a  condition  resulting  from 
the  absence  of  moisture,  a  cold  dry  cellar  can  be  enjoyed  during 
the  days  of  low  temperature  and  low  water  without  the  use  of 
either  a  refrigerating  machine  or  "heat  pump,"  or  a  water 
pump.  For  emergency,  however,  the  cellars  are  equipped  with 


76    ELEMENTARY  MECHANICAL  REFRIGERATION 

both  of  these  pumps,  and  the  walls  are  waterproofed  and  insu- 
lated as  a  provision  against  high  water  and  hot  weather.  When 
the  river  rises  sufficiently  high  the  water  will  flow  into  the  cellars 
instead  of  out  through  the  open  sewers,  and  when  the  outside 
temperature  rises  sufficiently  high  the  heat  will  flow  into  the  cel- 
lars instead  of  out  through  the  open  windows.  The  sewers  must  be 
accordingly  plugged  up  and  the  windows  closed.  This  does  not 
entirely  remedy  the  conditions,  however,  as  the  cellar  walls  are 
neither  perfectly  waterproofed  nor  perfectly  insulated  and  allow 
both  water  and  heat  to  percolate  in  from  the  outside. 

FLOW  OF  WATER  AND  HEAT  DUE  TO  DIFFERENCE   IN  LEVEL 

Water  flows  from  one  place  to  another  only  when  there  is  a 
difference  of  pressure  or  static  head.  Fifteen  feet  of  water  above 
the  level  of  the  cellar  floor,  since  a  column  of  water  one  foot  high 
and  one  square  inch  in  section  weighs  0.43  pounds,  will  exert  a 
pressure  of  6.45  pounds  per  square  inch  in  its  endeavor  to  get 
through  the  cellar  wall. 

Heat  flows  from  one  substance  to  another  only  when  there  is  a 
difference  in  temperature  or  thermal  head.  Seventy-two  degrees 
on  the  outside  of  the  cellar  walls  will  have  an  effective  thermal 
head  of  72°  — 36°  (the  inside  temperature)  thirty-six  degrees, 
tending  to  cause  a  heat  flow  through  the  cellar  walls. 

The  rate  at  which  either  water  or  heat  will  flow  from  one  place 
to  another  is  directly  proportional  to  the  difference  in  pressure, 
or  temperature,  tending  to  cause  the  flow  and  inversely  propor- 
tional to  the  resistance  opposing  that  flow.  If  proper  precautions 
are  taken  in  waterproofing  the  walls  of  the  cellar,  the  resistance 
encountered  by  the  water  will  be  so  great  that,  at  the  low  pressure 
at  which  it  is  trying  to  gain  entrance,  there  will  be  no  flow.  Ordi- 
nary precautions  against  encroachments  of  heat,  however,  can 
at  best  only  reduce,  and  never  entirely  prevent,  the  heat  from 
passing  through  the  walls.  While  thin  sheets  of  metal,  coatings 
of  asphalt  and  similar  materials  are  absolutely  impervious  to 
water  there  has  as  yet  been  no  material  found  which  is  anywhere 
near  a  perfect  non-conductor  of  heat. 

Since  water  always  flows  from  a  point  of  higher  to  one  of  lower 
pressure  or  level,  a  convenient  means  of  collecting  the  seepage 
in  the  cellars  is  by  draining  it  by  gravity  into  a  catch-basin  still 
lower  than  the  floors,  from  which,  in  the  case  shown  in  the  dia- 


SIMPLE  COMPARISONS 


77 


gram,  since  it  is  below  the  river  into  which  it  was  to  be  emptied, 
it  must  be  raised  by  a  pump.  The  water  pumping  system  (A. 
Fig.  34)  consists  of  a  suction  pipe  s,  a  pump  P  and  a  discharge 
pipe  d.  By  the  application  of  power  to  pump  P  the  water  in  the 
catch-basin  is  raised  23  feet  to  where  it  is  discharged  at  a  height 
of  7  feet  above  the  river,  into  which  it  flows  by  gravity. 


ITeet 


Dondenser  Pres.  180    Cooling  Water  on  70° 


Catch  Basin 


Fig.  34. — Diagram  Showing  Similarity  of  Systems  A  and  B  for  Extracting 
Water  and  Heat  Respectively 

Since  heat  always  tends  to  flow  from  a  point  of  higher  to  one 
of  lower  temperature,  a  convenient  means  of  collecting  the  heat 
which  filters  into  the  cellar  is  by  draining  it  by  gravity,  so  to  speak, 
into  a  coil  of  pipe  which  is  kept  still  lower  in  temperature  than  the 
cellar.  Since  this,  however,  is  lower  in  temperature  than  any 
cooling  water  available  for  carrying  it  away  (water  is  generally 
used  for  this  purpose),  its  temperature  must  be  raised  by  means 
of  a  heat  pump,  or  compressor.  This  heat  pumping  system,  B, 
is  composed  essentially  of  a  low-pressure  or  suction  side  s',  a 
compressor  P'  and  a  high-pressure  or  discharge  side  d'.  By 
the  expenditure  of  power  the  gas  pump  P'  was  employed  to 
raise  the  temperature  of  the  working  medium  from  that  of  the 
coil  s'  to  that  of  the  coil  d',  which  is,  in  this  case,  about  25° 
higher  than  the  temperature  of  the  cooling  water  into  which  the 
heat  must  flow  "by  gravity." 


78    ELEMENTARY  MECHANICAL  REFRIGERATION 

WORKING  PRESSURES 

The  working  pressures  encountered  are  fixed  by  working  condi- 
tions in  the  case  of  both  the  water  pump  and  the  heat  pump.  The 
water  entering  the  suction  pipe  of  the  water  pump  is  under  atmos- 
pheric pressure  and  a  sufficient  additional  pressure  must  be  ex- 
erted on  it  to  balance  the  weight  of  the  column  of  water  23  feet 
high  or  23X0.43  pounds,  about  10  pounds  per  square  inch.  If 
the  pump  were  under  the  column  of  water  it  would  have  to  exert 
this  amount  of  direct  pressure;  but  since  it  is  located  above  the 
column  of  water  it  must  create  a  vacuum  of  10  pounds,  reducing 
the  absolute  pressure  to  5  pounds,  so  that  the  atmospheric  pres- 
sure of  approximately  15  pounds  on  the  water  in  the  catch-basin 
will  exert  the  required  unbalanced  upward  pressure  of  10  pounds. 

In  the  case  of  the  heat  pump,  the  working  pressures  are  deter- 
mined by  the  working  temperatures,  viz.,  the  required  temperature 
in  the  cold-storage  compartment  and  the  temperature  of  the 
available  cooling  water  from  A .  The  whole  problem  depends  on  the 
temperatures  at  which  the  refrigerating  liquid  will  boil  under 
various  pressures  and  the  various  amounts  of  heat  that  must  be 
added  to  it  to  evaporate  the  liquid  at  the  boiling  point,  or  to  be 
abstracted  from  it  to  liquefy  the  vapor  at  the  boiling  point. 

EVAPORATING  TEMPERATURES 

Every  liquid  has  a  certain  characteristic,  fixed  boiling  tempera- 
ture or  boiling  point,  corresponding  to  each  pressure.  At  atmos- 
pheric pressure,  for  example,  water,  the  best  known  liquid,  has  a 
boiling  point  of  212°  Fahrenheit.  Alcohol  boils  under  atmos- 
pheric pressure  at  173°  Fahrenheit,  ether  at  96°  Fahrenheit, 
and  anhydrous  ammonia,  at  the  same  pressure,  boils  at  —  28.5° 
Fahrenheit.  This  temperature  is  quite  high  as  compared  with  the 
boiling  point  of  the  so-called  fixed  gases.  If  the  pressure  is  in- 
creased on  any  liquid  the  temperature  must  also  be  raised  in  order 
to  make  it  boil.  No  two  known  liquids  boil  at  the  same  tempera- 
ture under  the  same  pressure. 

Suppose,  for  example,  that  there  is  a  pound  of  liquid  ammonia 
in  the  coil  sf,  in  which  there  is  a  gas  pressure  of  55  pounds  by 
gauge.  The  temperature  of  the  cellar  is  36°  Fahrenheit.  When  the 
compressor  is  started  it  begins  to  pump  gas  out  of  the  coil,  just  as 
a  water  pump  lifts  water  out  of  the  catch-basin.  Now  under  55 
pounds  pressure  the  pound  of  liquid  ammonia  will  not  boil  because 


SIMPLE  COMPARISONS  79 

the  surrounding  temperature  is  36°  Fahrenheit,  which  is  two  de- 
grees less  than  the  boiling  point  of  ammonia  at  that  pressure. 
As  the  compressor  continues  to  pump  gas  out  of  the  coil  the  pressure 
will  eventually  become  less.  At  52.6  pounds  pressure  the  boiling 
point  of  ammonia  is  36°  Fahrenheit,  or  the  same  temperature  as  the 
cellar.  At  this  pressure  the  liquid  will  be  on  the  point  of  boiling, 
but  as  there  is  no  difference  in  temperature  between  the  ammonia 
within  the  pipes  and  the  atmosphere  outside  there  is  no  tendency 
for  heat  to  flow  from  the  atmosphere  to  the  liquid,  and  without 
heat  it  cannot  boil.  When  the  pressure  is  reduced  to  50  pounds, 
however,  the  boiling  point  will  have  been  reduced  to  34°  Fahren- 
heit and  there  will  be  a  difference  of  two  degrees,  tending  to  make 
heat  flow  from  the  air  of  the  cellar  to  the  ammonia.  This  slight 
difference  in  temperature  would  make  the  process  of  refrigerating 
a  cellar  very  slow  or  else  require  a  prohibitive  amount  of  pipe 
surface.  As  a  matter  of  fact,  about  ten  times  this  difference  in 
temperature  is  employed  in  practice.  With  a  cellar  temperature 
of  36°  Fahrenheit  and  a  difference  in  temperature  of  20°,  the  boil- 
ing point  of  the  liquid  would  be  16°  Fahrenheit  and  the  pressure 
required  to  give  this  temperature  29  pounds.  Under  these  con- 
ditions, from  eight  to  nine  feet  of  2-inch  pipe  would  evaporate  the 
one  pound  of  ammonia  in  an  hour.  In  other  words,  a  difference  of 
temperature  of  20°  Fahrenheit  will  cause  about  545  heat  units  per 
hour  to  flow  through  the  surface  afforded  by  eight  to  nine  lineal 
feet  of  2-inch  pipe. 

EVAPORATION  OF  WATER  AND  AMMONIA 

Similar  to  evaporation  of  ammonia  in  pipe  evils,  is  that  of  the 
water  in  a  watertube  boiler.  In  both  cases  the  lower  the  pres- 
sure and  the  hotter  the  temperature  outside,  the  more  liquid  will 
be  evaporated  per  square  foot  of  heating  surface  in  a  given  time. 
In  the  case  of  the  ammonia,  the  evaporating  liquid  cools  the  cellar, 
and  in  the  case  of  the  water,  it  refrigerates  the  fire-box. 

While  the  water  pump  has  but  one  function  to  perform,  that 
of  raising  the  water  from  the  catch-basin  to  the  discharge  level, 
the  compressor  must  not  only  raise  the  ammonia  gas  from  the 
expansion  coil  in  the  cellar  and  discharge  it  into  the  condenser 
on  the  roof  df,  but  also  raise  the  thermal  level  of  the  ammonia 
to  a  point  where  its  heat  can  gravitate  into  the  cooling  water,  which 
causes  the  ammonia  to  return  to  the  liquid  form.  If  the  cooling 


80    ELEMENTARY  MECHANICAL  REFRIGERATION 

water  is  supplied  to  the  condenser  at  70°  Fahrenheit  and  flows  away 
at  90°  Fahrenheit,  the  condensing  pressure,  according  to  the 
amount  of  cooling  water  and  cooling  surface  employed,  will  be 
from  180  to  190  pounds,  and  the  boiling  point,  or  temperature  at 
which  the  gas  will  liquefy,  corresponding  to  these  pressures,  will  be 
from  94°  to  97°  Fahrenheit.  The  maximum  temperature  attained 
by  the  gas,  however,  may  be  very  much  higher  than  this. 

Condenser  water  carries  away  the  heat  from  the  cellar,  though 
it  is  several  degrees  hotter  than  the  cellar,  just  as  the  river  car- 
ries away  the  water  from  the  cellar  though  it  is  several  feet  higher 
than  the  cellar.  The  compressor  raises  the  heat  through  a  certain 
number  of  degrees,  thereby  increasing  its  " thermal  head,"  just 
as  the  pump  raises  the  water  through  a  certain  number  of  feet, 
thereby  increasing  its  "  static  head." 

IV.    SIMPLE  COMPARISONS 

THERMAL  AND  STATIC  HEAD  AND  THE  FLOW  OF  HEAT  AND 

LIQUIDS 

In  following  out  the  present  comparison  it  should  be  remem- 
bered that  coal  is  simply  the  vehicle  for  bringing  us  heat  radiated 
by  the  sun  ages  ago.  By  absorption  of  solar  heat  a  chemical 
process  took  place  by  which  carbon-dioxide  from  the  atmosphere 
was  broken  up  in  the  plant  cells  of  the  vast  prehistoric  vegetable 
growths  and  formed  fixed  carbon  in  the  plant  tissues  and  free 
oxygen  exhaled  into  the  air.  In  the  process  of  combustion  of 
coal,  free  oxygen  from  the  air  again  combines  with  the  fixed  carbon 
of  the  plant  forming  carbon-dioxide,  and  the  long  imprisoned  solar 
heat  is  liberated.  Not  only  is  solar  heat  of  former  ages  made  to 
do  useful  work  through  the  evaporation  of  water  in  boilers,  but 
the  solar  heat  of  the  present  day  evaporates  the  moisture  which, 
precipitated  from  the  rain  clouds,  collects  to  form  cataracts  with 
power  to  turn  turbines.  'Not  only  is  prehistoric  solar  heat  used 
to  evaporate  water  in  boilers,  but  the  solar  heat  of  the  present 
could  be  used  in  the  same  way  if  its  rays  could  be  sufficiently  con- 
densed and  focused,  and  used  directly  for  the  production  of  steam 
power,  as  well  as  indirectly  for  production  of  water  power. 

It  is  not  altogether  unlikely  that  future  generations  will  see 
direct  solar  energy  so  utilized.  The  rapid  exhaustion  of  our  present 
fuel  deposits,  which  has  even  now  advanced  to  a  point  where  the 


SIMPLE  COMPARISONS  81 

gravity  of  the  situation  can  no  longer  be  ignored,  has  already 
directed  some  research  in  that  direction.  In  the  present  case, 
however,  it  is  sufficient  to  assume  that  the  steam  under  pressure 
in  the  boiler  has  been  raised  by  coal  and  that  the  atmospheric 
vapors  forming  the  clouds  have  been  raised  by  the  sun.  In  either 
case  energy  has  been  supplied  and  energy  must  be  withdrawn 
before  the  vapors  will  be  condensed  to  the  original  form  of  water. 
In  raising  the  vapor  from  the  surface  of  the  earth  to  the  clouds  a 
certain  amount  of  energy  is  expended.  In  passing  the  steam  from 
the  boiler  to  the  engine  there  is  also  a  considerable  expenditure  of 
energy. 

When  the  two  forms  of  vapor  have  reached  their  respective 
destinations,  however,  they  still  possess  a  considerable  energy  or 
capacity  for  doing  work  when  pressed  into  service  in  appropriately 
designed  machines.  When  the  atmospheric  vapor  has  been  di- 
vested of  a  sufficient  amount  of  its  latent  energy  it  condenses  into 
rain,  and  were  there  a  suitable  machine  at  hand  a  large  per  cent 
of  the  foot  pounds  of  work  developed  by  the  falling  rain  could  be 
utilized.  Since  comparatively  small  amounts  of  water  are  scat- 
tered over  large  areas,  man  must  content  himself  with  utilizing 
only  the  foot  pounds  remaining  in  the  rain  after  it  has  been  pre- 
cipitated and  collected  into  larger  masses  in  rivers  and  lakes, 
which,  though  many  feet  below  the  rain  clouds  where  it  possesses 
its  greatest  potential  energy,  may  yet  be  many  feet  above  the  level 
of  the  sea  from  which  it  arose  and  may  yet,  accordingly,  have  a 
considerable  capacity  for  performing  useful  work. 

WATER  POWER 

In  the  present  example  enormous  amounts  of  power  are  stored 
in  the  torrents  of  water  precipitated  on  the  great  watersheds  that 
feed  the  Northern  lakes  and  finally  flow  down  the  Niagara  River, 
a  part  to  turn  the  wheels  of  industry  and  a  part  to  dissipate  its 
energy  in  raising  the  temperature  of  the  rocky  gorge  below  the  falls. 

In  Fig.  35  is  shown  a  conventionalized  machine  for  utilizing 
a  part  of  the  energy  in  a  small  stream  of  water  diverted  from  the 
Niagara  River  above  the  Falls.  While  theoretically  a  modern 
vertical  turbine  might  have  been  employed  in  this  analogy,  for 
simplicity  of  detail  and  similarity  of  comparison  a  bucket  conveyor 
is  shown.  Water  from  the  duct  leading  from  the  river  is  discharged 
into  the  buckets  near  the  top  of  a  sprocket  wheel.  The  weight 


82    ELEMENTARY  MECHANICAL  REFRIGERATION 

of  the  descending  water  in  the  upper  chain  of  buckets  turns  the 
lower  shaft  carrying  a  second  chain  of  buckets  so  arranged  as  to 
elevate  the  water  accumulating  in  the  shaft  below  the  level  of  the 
river,  and  discharge  it  into  a  trough  near  the  point  of  discharge 
of  the  upper  chain  at  such  a  height  that  it  can  flow  away  by  gravity 
into  the  river. 

The  power  available  in  any  machine  is  the  product  of  the  force 
acting  and  the  space  acted  through.  In  the  present  example  the 
distance  between  the  point  of  charging  and  that  of  discharging 
the  buckets  is  about  50  feet,  so  that  every  thousand  pounds  of 
water  discharged  will  have  exerted  50,000  foot  pounds,  every 
33,000  of  which  per  minute  is  equivalent  to  a  horsepower  of  work, 
and  every  778  of  which  is  equivalent  to  one  B.t.u.  of  heat  (50,000 
pounds  per  minute  =  1.515  H.P.or  64.27  B.t.u.).  In  this  example 
it  is  obvious  that  the  higher  the  point  at  which  the  water  can 
be  received  and  the  lower  the  point  at  which  it  can  be  discharged, 
the  more  power  will  be  developed. 

The  amount  of  power  to  be  expended  in  raising  the  water  from 
the  shaft  depends  not  only  on  the  number  of  pounds  of  water  to 
be  raised  in  a  given  time,  but  also  on  the  number  of  feet  through 
which  it  is  to  be  raised.  If  the  water  is  running  into  the  shaft  at 
different  levels  it  is  obvious  that  less  power  will  be  required  if 
provision  is  made  for  collecting  it  and  conducting  it  into  the  con- 
veyor at  about  the  level  at  which  it  enters  than  if  it  were  all 
allowed  to  flow  to  the  bottom  of  the  shaft.  If  the  height  of  the 
point  of  discharge  be  more  than  just  sufficient  to  allow  the  water 
to  flow  away  to  the  river,  foot  pounds  of  work  will  be  unnecessarily 
expended.  Similarly,  if  the  point  of  discharge  of  the  water  from 
the  upper  buckets  is  higher  than  necessary  to  enable  the  water  to 
flow  away  freely,  loss  of  power  will  result.  Since  the  water  dis- 
charged from  both  sets  of  buckets  must  all  flow  into  the  river,  the 
points  of  discharge  may  be  on  the  same  level,  as  shown,  or  at 
different  levels,  providing  both  levels  are  above  that  of  the  river. 

PUMPING  WATER  AND  HEAT 

The  analogy  is  apparent.  The  source  of  the  water  available 
for  producing  power  is  160  feet  above  the  bottom  of  the  shaft, 
giving  it  a  potential  energy  which  may  be  said  to  be  equivalent 
to  that  of  steam  having  a  temperature  of  370°  Fahrenheit.  This 
steam  may  be  expanded  to  the  lowest  pressure,  or  the  heat  may 


84    ELEMENTARY  MECHANICAL  REFRIGERATION 

be  allowed  to  flow  to  the  lowest  temperature  at  which  it  can  still 
flow  away  into  the  river  of  condenser  water.  If  this  temperature 
is  126°  Fahrenheit  the  corresponding  pressure  will  be  26  inches 
vacuum. 

This  falling  of  temperature  resulting  from  the  conversion  of 
heat  into  work,  in  the  steam  engine  shown  on  the  left,  is  repre- 
sented by  the  steam  indicator  diagram  shown  on  the  right,  tem- 
peratures at  any  point  of  which  are  approximately  indicated  by 
the  thermometer. 

The  water  to  be  removed  from  the  pit  represents  heat  to  be 
removed  from  the  lower  levels  of  temperature  found  in  cold-storage 
compartments.  This  heat  has  to  be  elevated  almost  to  the  same 
level  at  which  heat  from  the  engine  is  exhausted,  because  of  the  fact 
that  the  most  satisfactory  disposition  of  the  heat  from  both  sources 
is  to  let  it  flow  into  the  same  river  of  condenser  water.  The  lower 
the  point  of  discharge  the  more  power  will  be  available  in  driving 
the  chain  per  pound  of  water,  and  the  less  power  will  be  required 
to  raise  a  given  quantity  of  water  by  the  driven  chain.  The  lower 
the  temperature  in  the  condenser  water  the  more  power  will  be 
developed  in  the  driving  steam  engine  per  pound  of  steam  expended 
and  the  less  the  power  required  to  raise  a  given  quantity  of  heat 
in  the  driven  refrigerating  machine.  In  other  words,  the  efficiency 
of  the  driving  machine  depends  directly  on  the  difference  in  head 
of  the  water  entering  and  leaving  the  buckets,  just  as  that  of  a 
steam  engine  depends  on  the  difference  in  temperature  between 
the  steam  in  the  boiler  and  that  in  the  condenser.  Similarly,  the 
efficiency  of  the  driven  machine  increases  directly  as  the  difference 
in  head  between  the  water  leaving  and  entering  the  buckets  de- 
creases, just  as  that  of  a  compression  refrigerating  machine 
increases  as  the  difference  in  temperature  between  the  gas  in  the 
condenser  and  that  in  the  cooler  decreases.  Since  the  pressure 
of  steam  at  the  lowest  point  to  which  it  is  practical  to  expand 
it  is  considerably  above  that  of  the  refrigerating  medium  lique- 
fying at  the  lowest  temperature  that  available  cooling  water 
will  allow,  it  is  found  economical  in  practice  to  first  permit  the 
heat  from  the  refrigerating  medium  to  flow  into  the  cooling  water, 
after  which  its  thermal  level,  or  temperature,  even  after  being 
raised  by  heat  from  the  refrigerating  machine  condensers,  will 
still  be  sufficiently  low  to  allow  heat  from  the  steam  engine  con- 
densers to  gravitate  into  it.  The  diagram  illustrates  this  to  the 


SIMPLE  COMPARISONS  85 

extent  of  showing  that  the  point  of  discharge  of  the  water  from 
the  driving  conveyor  is  slightly  above  that  of  the  driven 
conveyor.  This  cooling  water  containing  the  heat  from  the 
steam  condenser  is  shown  in  the  diagram  flowing  away  with 
the  water  from  the  driving  conveyor  and  that  from  the  re- 
frigerating machine  condenser  with  the  water  from  the  driven 
conveyor. 

The  two  sets  of  expansion  coils,  El  and  E2,  located  the  one 
above  the  other,  represent  the  different  thermal  levels  or  tempera- 
tures at  which  the  heat  is  absorbed  in  two  cold-storage  rooms. 
The  different  temperatures  at  which  these  two  storage  rooms  are 
to  be  maintained  is  also  represented  by  the  height  of  the  spouts 
which  deliver  the  water  seeping  through  the  walls  of  the  shaft 
into  the  driven  conveyor.  The  operation  of  the  compressor  of  the 
refrigerating  machine  shown  on  the  left  is  also  represented  in 
the  compressor  indicator  card  shown  on  the  right, — heights  in  feet, 
temperatures  in  degrees,  and  corresponding  pressures  in  pounds, 
being  represented  on  the  three  scales  also  shown  at  the  right. 

LEAKS 

To  complete  the  analogy  it  is  necessary  to  remember  that  in 
the  operation  of  the  driving,  as  well  as  the  driven,  chain  of  buckets 
there  are  losses  by  friction  in  the  bearings  as  in  a  steam  engine 
and  compressor;  losses  in  capacity  due  to  imperfect  filling  of  the 
buckets  corresponding  to  imperfect  cylinder  filling  in  a  com- 
pressor ;  losses  due  to  leaks  in  the  buckets  corresponding  to  leaks 
by  valves  and  pistons  of  the  steam  engine  and  compressor.  In  the 
case  of  the  best  steam  power  plants,  all  but  about  15  per  cent  of  the 
heat  " leaks  away"  without  performing  any  useful  work.  In  the 
average  steam  plant  all  but  about  6  or  8  per  cent  is  lost,  so 
that  it  is  of  the  utmost  importance  that  this  small  remaining  per 
cent  of  heat  be  utilized  to  the  best  possible  advantage  in  the 
refrigerating  machine. 

WORKING  LIMITS 

The  next  most  important  detail  to  be  considered  after  that  of 
keeping  the  compressor  in  good  mechanical  repair — that  is,  to  see 
that  the  lower  buckets  do  not  leak,  realizing  that,  on  account  of 
the  small  per  cent  of  useful  work  resulting  from  the  expenditure 
of  energy  in  the  prime  mover,  a  given  loss  in  the  driven  machine 
is  of  much  greater  importance  than  the  same  loss  in  the  driving 


86    ELEMENTARY  MECHANICAL  REFRIGERATION 

machine — is  to  see  that  the  condenser  pressure  or  point  of  dis- 
charge of  the  water  is  as  low  as  possible  and  that  the  expansion  coil 
pressure  is  as  high  as  possible,  or  that  the  buckets  pick  up  the 
water  at  as  high  a  level  as  possible.  Assuming  that  the  point  of 
discharge  of  the  water  be  100  feet  above  the  bottom  of  the  shaft, 
100  foot-pounds  of  work  must  be  expended  in  a  theoretically  per- 
fect machine  to  elevate  a  single  pound  of  water.  At  the  efficiency 
of  the  average  ammonia  compressor,  from  25  to  35  additional  foot- 
pounds would  have  to  be  supplied  to  make  up  for  leaks  and  other 
losses.  If  the  water  all  enters  the  shaft  at  B,  a  point  only  65 
feet  below  the  point  of  discharge  or  35  feet  above  the  bottom  of 
the  shaft  and  means  of  directing  it  into  the  buckets  at  this  level  be 
devised,  only  65  foot-pounds  in  a  theoretically  perfect  machine, 
or  only  from  81  to  88  foot-pounds  in  a  machine  of  the  efficiency  of 
an  ammonia  compressor,  need  be  expended  to  do  the  same  amount 
of  work. 

Assuming,  similarly,  that  the  refrigerating  machine,  repre- 
sented by  the  chain  of  buckets,  discharges  the  heat  at  a  tempera- 
ture 100°  Fahrenheit  above  that  of  the  colder  refrigerator  coil 
corresponding  to  the  bottom  of  the  shaft,  wilich  temperature,  for 
the  sake  of  similarity,  may  be  taken  at  0°  Fahrenheit,  the  horse- 
power per  ton  of  refrigeration  would  be  1.2194.*  Interpolating 
to  find  the  temperature  from  which  heat  equivalent  to  a  ton  of 
refrigeration  can  be  raised  by  the  expenditure  of  half  that  amount 
of  power,  or  0.6097  horse-power  per  ton,  a  cooler  temperature  of 
approximately  42J/2°  Fahrenheit  is  obtained. 

If  a  refrigerating  plant  is  so  operated  that  this  heat  which 
enters  the  refrigerator  at  such  a  temperature  that  it  can  be  ab- 
sorbed by  a  refrigerant  at  42^°  Fahrenheit  has  to  be  absorbed  at 
0°  Fahrenheit,  in  other  words,  if  the  plant  is  operated  at  16  pounds 
back  pressure  when  it  could  be  operated  at  61  pounds,  one-half 
the  power  will  be  as  needlessly  expended  as  would  be  the  case  if 
the  water  entering  the  shaft  at  a  height  of  50  feet  were  allowed 
to  flow  to  the  bottom,  requiring  the  buckets  to  lift  it  100  feet  in- 
stead of  50  feet. 

The  example  just  cited  need  be  none  the  less  significant  be- 
cause of  the  unusual  back  pressure  of  61  pounds  gauge.  Except 
for  selecting  temperatures  to  agree  with  the  feet  head  of  water 

*  See  table  of  horse-power  per  ton  of  refrigeration — Schmidt,  "Compend. 
of  Mechanical  Refrigeration,"  page  449. 


SIMPLE  COMPARISONS 


87 


already  mentioned  in  the  analogy,  lower  temperatures  might  just 
as  well  have  been  considered,  for  example : 

The  horsepower  required  per  ton  of  refrigeration  when  the 
back  pressure  is  four  pounds  gauge  corresponding  to  a  temperature 
of  20°  Fahrenheit,  and  the  same  head  pressure  of  200  pounds 
gauge  corresponding  to  a  temperature  of  100°  Fahrenheit,  is  1.6090. 
Again  interpolating  in  the  table  we  find  that  half  this  power 
per  ton  would  be  expended  when  the  back  pressure  is  38  pounds, 
corresponding  to  a  refrigerator  temperature  of  24.4°  Fahrenheit. 

For  convenience  in  comparison  the  foregoing  figures  are  shown 
in  tabular  form  in  Table  II. 


TABLE  II.— TABLE  SHOWING  CONDITIONS  UNDER  WHICH  A  TON  OF  REFRIG- 
ERATION CAN  BE  PRODUCED  BY  THE  EXPENDITURE  OF  ONE-HALF  THE 
POWER  REQUIRED  UNDER  OTHER  CONDITIONS. 


REFRIGERATOR 

CONDENSER 

HORSE-POWER 

Pressure, 
Lbs.  G. 

Temperature, 
F° 

Pressure, 
Lbs.  G. 

Temperature, 

v 

Per  Ton 
Refrigeration 

Per  Cent. 

16 
61 

0° 

42^° 

200 

100° 

1.2194 
0.6097 

100 
50 

4 
38 

—20° 

24.4° 

200 

100° 

1.6090 
0.8045 

100 
50 

While  from  the  foregoing  it  would  seem  inexcusable  to  operate 
a  refrigerating  plant  at  a  lower  back  pressure  than  actually  re- 
quired to  produce  the  desired  temperatures,  yet  it  is  probable 
that  not  over  ten  per  cent  of  the  plants  in  commercial  operation 
today  are  operating  under  anywhere  near  the  advantageous  con- 
ditions with  regard  to  back  pressure  that  they  should. 

The  problem  becomes  less  easy  of  solution  as  the  number  of 
different  temperatures  increases.  Again  following  out  the  chain 
pump  analogy,  let  an  extreme  case  be  assumed  in  which  90  per 
cent  of  the  water  flowed  into  the  shaft  at  a  height  of  50  feet  from 
the  bottom,  and  the  remaining  10  per  cent  at  the  bottom.  The 
theoretical  amount  of  energy  required  to  raise  one  ton,  or  2,000 
pounds,  of  water  from  the  levels  at  which  it  runs  in  would  be 
2,000 X. 90 X 50+2,000 X.  10X100  =  110,000  foot  pounds.  If  the 
water  be  allowed  to  flow  to  the  bottom  of  the  shaft,  however,  it 
will  take  2,000X100  =  200,000  foot  pounds,  or  81.8  per  cent  more 
power  than  by  the  former  method.  If  90  per  cent  of  a  ton  of 


88    ELEMENTARY  MECHANICAL  REFRIGERATION 

refrigerating  duty  be  performed  at  24.4°  Fahrenheit,  and  38 
pounds  back  pressure  and  the  remaining  10  per  cent  of  the  ton  at 
—  20°  Fahrenheit  and  four  pounds  back  pressure,  the  actual 
amount  of  power  required  will  be  .90 X. 8045 +.10X1. 609  =  .8849 
horsepower;  but  if  the  expansion  coils  for . producing  both  tem- 
peratures are  connected  into  a  common  suction  line  so  that  all 
of  the  work  of  refrigeration  has  to  be  done  at  —  20°  Fahrenheit  and 
four  pounds  back  pressure,  the  power  required  will  be  1.6087,  or, 
as  in  the  case  of  the  water,  81.8  per  cent  more  than  by  the  former 
method. 

To  avoid  expending  this  additional  amount  of  power  the  same 
solution  presents  itself  in  both  cases  in  question.  Two  separate 
machines  may  be  installed,  one  to  perform  the  more  difficult  work 
of  raising  the  lesser  amounts  of  water  or  heat  through  the  greater 
distance,  and  the  other  to  perform  the  less  difficult  work  of  raising 
the  larger  amount  of  water  or  heat  through  the  lesser  distance. 
Either  two  compression  or  two  absorption  machines  may  be 
detailed  to  the  two  duties,  or,  on  account  of  the  higher  efficiency 
of  the  absorption  over  the  compression  machine  when  operating 
on  very  low  temperatures,  the  work  may  be  allotted  to  one  com- 
pression and  one  absorption  machine;  or  a  unit  may  be  employed 
of  the  proper  capacity  for  raising  all  of  the  water  or  heat  from  the 
higher  level,  while  a  second  unit  is  employed  to  raise  the  lesser 
amounts  of  water  or  heat  from  the  lower  level  to  the  middle  level 
where  the  other  machine  begins  to  operate. 

In  refrigerating  plants  equipped  with  a  single  double-acting 
compressor,  or  two  single-acting  compressors,  the  high  and  low 
temperature  loads  are  so  proportioned  that  one  end  of  a  double- 
acting  compressor  can  be  made  to  handle  the  high  temperature 
load  and  the  other,  the  low;  or  in  the  case  of  two  single-acting 
compressors,  the  load  may  be  similarly  divided  between  the  two 
machines,  with  the  additional  advantage  over  the  use  of  one 
double-acting  compressor  that,  if  the  loads  are  not  properly 
balanced,  the  speeds  of  the  machines  may  be  varied  to  suit. 

Still  another  way  out  of  the  difficulty,  and  one  which  avoids 
many  complications  arising  in  the  preceding  case,  is  to  allow  the 
buckets  to  run  to  the  lower  level  and  pick  up  such  load  as  there 
may  be,  whether  large  or  small,  after  which  additional  load  is 
taken  on  at  the  higher  level.  By  this  method  the  load  is  picked 
up  at  whatever  level  it  happens  to  occupy,  and  the  expenditure 


SIMPLE  COMPARISONS  89 

of  the  additional  energy  required  to  raise  the  greater  part  of  the 
load  from  the  lower  level  is  divided. 

MULTIPLE  EFFECT  REFRIGERATING  MACHINE 

When  applied  to  the  compressor  of  a  refrigerating  machine,  the 
method  is  to  admit  the  low  pressure  gas  returning  from  the  coldest 
expansion  coils  directly  into  the  cylinder.  When  a  sufficient  part 
of  the  stroke  has  been  completed  to  provide  for  the  low-pressure 
gas,  a  secondary  suction  valve  is  opened  and  the  higher-pressure 
gas  from  the  higher  temperature  expansion  coils  is  introduced. 
The  low-pressure  gas  is  prevented  from  returning  through  its 
suction  line  by  the  closing  of  the  low-pressure  suction  valves,  or 
simply  a  check  valve  in  the  low-pressure  line.  Every  different 
plant  is  unquestionably  a  problem  in  itself,  but  whatever  the 
plant,  one  of  the  most  important  questions  to  be  borne  in  mind 
every  hour  of  the  twenty-four  is:  Is  the  compressor  operating  at 
the  highest  possible  back  pressure  and  lowest  possible  condenser 
pressure? 


CHAPTER  VI 
ICE-MAKING  SYSTEMS 

NEXT  in  importance  to  the  direct  utilization  of  refrigeration 
for  the  cooling  of  perishable  products  is  that  of  artificial  ice  mak- 
ing. While  there  are  a  number  of  systems  which  may  in  the  fu- 
ture modify  present  methods,  practically  all  the  ice  produced 
to-day  is  made  by  either  the  can  or  the  plate  system. 

THE  CAN  SYSTEM 

In  general,  the  process  of  manufacturing  can  ice  consists  of 
immersing  cans  of  water  in  brine  tanks  not  unlike  those  employed 
for  cooling  brine  for  brine-circulating  systems.  First,  the  specific 
heat,  then  the  latent  heat  of  the  water  is  given  up  to  the  brine, 
which,  in  turn,  passes  it  on  to  the  liquid  refrigerant,  most  com- 
monly ammonia. 

DISTILLING  APPARATUS 

Since  any  impurities  in  solution  or  suspension  in  the  water  fed 
to  the  cans  are  eventually  frozen  into  the  ice,  it  becomes  necessary 
to  use  water  as  nearly  pure  as  possible.  The  purity  of  ice,  how- 
ever, is  somewhat  erroneously  judged  by  its  transparency.  Im- 
pure ice  may  be  almost  entirely  transparent  while,  on  the  other 
hand,  pure  ice,  except  for  the  presence  of  air  which  produces 
whiteness,  may  be  unsalable  because  of  its  opaque  appearance. 
To  remove  air  as  well  as  both  organic  and  inorganic  impurities 
from  the  water,  distilling  systems  are  ususally  employed  in  can 
ice-making  plants.  As  large  quantities  of  water  must  be  evap- 
orated to  make  the  steam  necessary  for  driving  the  ammonia  com- 
pressors and  other  machinery  of  an  ice-making  plant,  it  follows 
that  the  boilers  and  engine  logically  constitute  a  part  of  the 
water-distilling  system. 

HIGH  PRESSURE  SYSTEM 

Fig.  36  illustrates  diagrammatically  the  simple  or  high-pressure 
system  commonly  employed  in  making  can  ice.  As  a  steam  boiler 
is  virtually  a  thermal  filter  which  separates  out,  in  the  form  of 
incrustation  and  sludge,  most  of  the  impurities  brought  to  it  in 
the  feed  water,  the  water  supply  for  an  ice  plant  should  be  selected 


ICE-MAKING  SYSTEMS 


91 


with  particular  care,  especially  as  it  often  becomes  necessary  to 
supply  raw  " make-up"  water  to  the  storage  tank  when  the  supply 
of  distilled  water  runs  short. 

As  shown  in  the  illustration,  the  exhaust  steam  from  the  engine 
driving  the  compressor  passes  first  to  the  grease  separator  in 
which  it  is  freed  of  a  large  part  of  the  entrained  lubricating  oil 
by  impinging  upon  baffle  plates.  From  the  grease  separator  it 

/-\  Cooling  Water 


Back 
Pressure  Valve 


Supply  5team~°~l 


Ammonia  6as 
Inlet 

c 

i 

Ammonia  Liquid  5 
Outlet 

Ammonia  3 

^  Condense^ 

1   w'""  '  fl 

is  ,  — 

••>:WaterRegulatdr-^-^-"^- 


Fig.  36- — Simple  High  Pressure  Distilling  System 

passes  to  the  steam  condenser  from  whence,  after  being  condensed, 
it  flows  to  the  reboiler,  skimmer  and  hot-water  storage  tank. 
From  the  latter  the  hot  distilled  water  is  allowed  to  flow  as  re- 
quired into  the  water  cooler;  entering  at  the  bottom  and  passing 
up  through  a  series  of  pipes  it  is  here  cooled  by  water  flowing  down 
over  the  outside  of  the  pipes.  From  the  water  cooler  it  passes 
to  a  charcoal  filter  or  deodorizer  and  through  a  hose  to  the  can 
filler.  When  frozen  the  ice  is  removed  from  the  cans  by  spraying 
with  hot  water,  after  which  it  is  allowed  to  gravitate  down  an 
inclined  chute  into  the  ice-storage  room. 

In  traversing  that  part  of  the  system  between  the  steam  con- 
denser and  the  ice  cans  the  distilled  water,  after  having  been  freed 
from  air  and  other  gases  in  the  reboiler,  is  not  again  allowed  to 


92    ELEMENTARY  MECHANICAL  REFRIGERATION 


come  in  contact  with  air;  the  reason  for  this  is  twofold:  First, 
any  air  entering  into  solution  in  the  distilled  water  will  separate 
out  in  the  form  of  minute  bubbles  during  the  freezing  process  and 
give  the  ice  an  opaque  appearance;  second,  distilled  water  in  the 
presence  of  air  is  very  corrosive  to  iron,  and  should  they  be  allowed 
to  come  in  contact  with  any  part  of  the  system  not  thoroughly 
protected  by  galvanizing,  a  sufficient  amount  of  iron  would  be 
dissolved  to  discolor  the  ice. 

FREEZING  TIME  REQUIRED  FOR  CAN  ICE 

With  brine  at  14  degrees  the  average  time  of  freezing  different- 
sized  blocks  of  can  ice  is  as  shown  in  Table  III. 

TABLE   III.     TIME   REQUIRED   FOR   FREEZING   CAN   ICE 


Size  of  Can, 
Inches 

Weight  of 
Ice,  Pounds 

Freezing 
Time,  Hours 

Size  of  Can, 
Inches 

Weight  of 
Ice,  Pounds 

Freezing 
Time,  Hours 

6  x  12  x  26 
8  x  16  x  32 
8  x  16  x  42 

50 
100 
150 

15—25 
30—50 
•30—50 

11x22x32 
11  x  22x44 
11x22x57 

200 
300 
400 

50—72 
50—72 
50—72 

While  no  exact  rule  can  be  formulated  for  expressing  the  freez- 
ing time  in  terms  of  difference  in  temperature  between  the  brine 
and  the  freezing  water  in  the  can,  because  of  the  fact  that  the  heat- 
transmitting  surface  of  the  freezing  water  is  decreasing  and  the 
insulating  effect  of  the  ice  forming  is  increasing,  it,  nevertheless, 
has  been  claimed  by  some  that  the  time  required  for  freezing  can 
ice  with  brine  at  the  usual  temperature  varies  directly  as  the  square 
of  the  thickness  of  the  cake  of  ice.  On  this  basis  the  relative  time 
of  freezing  6-inch  and  11-inch  blocks  would  be  as  36  is  to  121,  or 
allowing  50  hours  for  the  latter,  the  former  should  freeze  in  14.9 
hours. 

THE  PLATE  ICE  SYSTEM 

Where  reasonably  pure  water  is  available  the  can  system  with 
its  distilling  apparatus  is  often  replaced  by  the  plate-ice  system. 
The  important  requisite  of  any  ice-making  system  from  a  commer- 
cial standpoint  is  its  ability  to  produce  marketable  ice,  which, 
unfortunately,  often  depends  more  upon  the  appearance  than  upon 
the  purity  of  the  product.  In  the  can  system  practically  all  solid 
impurities  are  left  behind  in  the  process  of  distillation,  air  and 
foreign  gases  being  expelled,  by  violent  boiling  in  the  reboiler. 
In  the  plate  system  the  keeping  of  the  product  free  from  both 


ICE-MAKING  'SYSTEMS  93 

solid  and  gaseous  impurities  is  almost  wholly  dependent  upon 
the  agitation  of  the  freezing  water.  Snow  may  be  pure,  but  it  is 
white  because  of  the  presence  of  a  large  number  of  minute  air 
spaces  between  the  crystals  of  ice.  Gases,  in  general,  are  sol- 
uble in  liquids,  the  degree  of  solubility  varying  widely  with 
the  temperature  and  pressure;  the  higher  the  pressure  and  the 
lower  the  temperature,  the  greater  the  amount  of  gas  a  liquid 
will  absorb.  In  the  case  of  freezing  water,  however,  the  air  is 
driven  out  of  solution  and  collects  in  the  form  of  little  bubbles 
on  the  freezing  surface.  These  bubbles  will  finally  be  frozen  into 
the  ice  if  not  forcibly  dislodged. 

INORGANIC  IMPURITIES 

In  the  manufacture  of  plate  ice  the  principal  inorganic  impuri- 
ties to  be  guarded  against  are  the  salts  of  iron  which  give  a  reddish 
discoloration,  and  the  carbonates  and  sulphates  of  lime  and  mag- 
nesia which  produce  a  slight  cloudiness.  Unless  large  quantities 
of  magnesium  carbonate  or  carbonate  of  iron  are  present  the  effects 
of  these  impurities,  as  well  as  that  of  air,  can  be  overcome  by  in- 
creased agitation.  In  the  case  of  carbonates  of  either  magnesia 
or  iron,  increased  air  agitation  may  tend  to  increase  the  discolora- 
tion through  the  hydrating  of  the  former  and  the  oxidizing  of  the 
latter.  This  difficulty  may  be  overcome,  however,  by  the  substi- 
tution of  mechanical  for  air  agitation. 

OPERATION  OF  PLATE  SYSTEM 

Mechanically,  a  plate  plant  is  so  constructed  that  the  raw 
undistilled  water  to  be  frozen  is  brought  in  contact  with  plates  of 
sheet  metal  bolted  to  either  brine  or  direct  expansion  coils,  in  which 
a  sufficiently  low  temperature  is  maintained  to  bring  about  the 
necessary  heat  transfer  from  the  water  at  32°.  These  plates, 
which  are  not  usually  less  than  14  feet  long  by  1Q  feet  deep, 
are  submerged  in  the  plate  tanks.  The  refrigerating  agent, 
whether  brine  or  ammonia,  is  allowed  to  flow  through  the  coils 
until  ice  has  accumulated  to  a  thickness  of  12  to  14  inches  on 
the  plate.  The  cold  brine  or  ammonia  is  then  shut  off  and  hot 
brine  or  ammonia  is  circulated  through  the  coils  until  the  ice  is 
loosened  from  the  plate  and  floats  free  in  the  water.  Chains  are 
then  fished  around  the  cake  and  it  is  hoisted  from  the  tank  by  a 
traveling  crane  and  carried  to  a  tilting  table,  where  it  is  carefully 


94    ELEMENTARY  MECHANICAL  REFRIGERATION 

deposited  to  avoid  breaking.  Here  it  is  sawed  into  cakes  of  the 
required  size,  by  two  gangs  of  traveling  circular  saws,  one  traveling 
lengthwise  and  the  other  crosswise  of  the  table.  Because  of  being 
frozen  from  water  at  32°  Fahrenheit,  with  which  it  is  always  in 
contact,  the  actual  temperature  of  plate  ice  is  not  as  low  as  that 
of  can  ice,  the  temperature  of  which  is  limited  only  by  the  tempera- 
ture of  the  brine.  On  account  of  this  fact,  plate  ice  is  less  likely  to 
be  brittle,  has  less  tendency  to  freeze  together  and,  therefore,  can 
be  stored  more  readily  than  can  ice. 

CENTER-FREEZE  SYSTEM 

The  factor  which  limits  the  application  of  the  plate  system  is 
the  time  required  for  freezing,  the  absorption  of  heat  having  to 
take  place  in  this  case  wholly  from  one  side  while  that  in  a  can  is 
from  five  sides.  This  disadvantage  has  been  overcome  to  some 
extent  in  the  "Center-freeze"  system,  in  which  the  plate  of  ice 
is  frozen  on  a  comb-formed  series  of  vertical  brine  pipes  attached 
at  the  top  to  suitable  feed  and  return  headers.  In  this  system  heat 
is  absorbed  radially  from  all  directions  by  each  pipe  and,  being 
located  in  the  center  of  the  plate  of  ice,  the  total  thickness  of  ice 
frozen  through  need  never  be  over  half  that  of  the  usual  plate 
system  producing  a  plate  of  the  same  thickness.  When  the  plate 
of  ice  is  frozen  to  the  desired  thickness  it  is  melted  loose  from  the 
freezing  pipes  as  in  the  preceding  case. 

It  is  claimed  by  the  promoters  of  this  system  that  the  time  of 
freezing  is  considerably  less  than  half  that  of  the  usual  plate  sys- 
tem operating  with  brine  of  the  same  temperature.  As  a  matter 
of  fact,  it  would  be  expected  to  be  less,  in  the  ratio  of  the  square 
of  the  thicknesses  frozen  through,  were  there  the  same  amount 
of  heat-absorbing  surface  in  each  case.  • 

In  other  words,  where  130  hours  is  required  to  freeze  plate  ice 
by  the  usual  method,  it  would  be  expected  that,  on  the  basis  of 
equal  cooling  surface,  only  about  33  hours  would  be  required. 
As  a  matter  of  fact,  with  the  usual  surface  and  zero  brine  it  is 
claimed  that  1 1  inches  of  plate  ice  can  be  frozen  by  this  method 
in  36  hours. 

EVAPORATORS  AND  VACUUM  DISTILLING  APPARATUS 

In  can  ice-making  plants  of  over  ten  tons  daily  capacity  and 
employing  engines  of  the  Corliss  type,  there  is  seldom  sufficient 


ICE-MAKING  SYSTEMS  95 

sweet  or  distilled  water  from  the  exhaust-steam  condensers  to  sup- 
ply the  freezing  tanks.  This  prohibits  maximum  steam  economy 
where  the  usual  high-pressure  distilling  apparatus  is  employed. 
For  instance,  assuming  a  100-ton  ice  plant  requiring  2.75  horse- 
power per  ton  and  operated  by  a  four-valve  engine  using  30  pounds 
of  steam  per  horsepower  per  hour,  the  steam  required  for  the 
engine  would  be  about  100  tons  per  24  hours.  The  auxiliaries 
and  reboiler,  together  with  the  usual  condensation  and  leakage 
past  the  valves  of  the  engine  and  auxiliaries,  would  probably  amount 
to  25  tons,  making  in  all  about  125  tons  of  steam.  This  amount 
of  steam  would  supply  sweet  water  for  the  100-ton  can  plant  and 
allow  for  a  loss  of  20  per  cent  between  the  exhaust  pipe  and  ice 
cans.  If,  however,  the  loss  were  as  much  as  24  per  cent,  which 
might  readily  happen,  the  make-up  water  required  would  amount 
to  about  8,000  pounds  per  24  hours.  This  quantity  of  steam  at  a 
cost  of  20  cents  per  thousand  pounds  would  be  worth  $1.60  per 
day. 

If  the  engine  employed  were  of  the  Corliss  type,  simple,  non- 
condensing  and  having  a  steam  consumption  of  28  pounds  per 
horsepower-hour,  the  steam  required  to  drive  the  compressor 
would  be  about  92.4  tons.  Hence,  the  amount  of  make-up  water, 
even  on  the  basis  of  20  per  cent  waste,  would  be  13,200  pounds, 
which  at  20  cents  per  thousand  pounds  would  cost  $2.64  per 
day. 

From  the  foregoing  it  is  obvious  that  to  employ  engines  of 
lower  steam  consumption  results  in  developing  an  ice-making 
capacity  in  excess  of  the  amount  of  sweet  water  available.  This 
excess  capacity  over  that  required  to  freeze  the  available  distilled 
water  may  be  employed  to  freeze  ice  in  a  plate  tank,  or  the  deficit 
in  sweet  water  necessary  to  supply  the  can  plant  may  be  made  up 
by  means  of  evaporators. 

COMBINED  CAN  AND  PLATE  ICE  PLANT 

A  combination  can  and  plate  plant,  designed  to  satisfy  the 
first  of  these  conditions,  is  illustrated  diagrammatically  in  Fig.  37. 
Leaving  the  ammonia  compressor,  the  gas  is  first  discharged  into 
the  two  pressure  tanks  where  any  entrained  oil  is  deposited. 
From  there  it  passes  through  pipe  B  to  the  condensers  and  after 
liquefying  it  flows  through  pipe  D  to  the  liquid  receiver.  The  line 
from  the  bottom  of  the  liquid  receiver  branches  off,  line  F  supply- 


96    ELEMENTARY  MECHANICAL  REFRIGERATION 


ICE-MAKING  SYSTEMS 


97 


ing  the  can  plant  and  ice-storage  room  and  E  supplying  the  plate 
plant.  The  water  forecooler  is  fed  in  series  with  the  plate  plant, 
after  passing  through  which,  the  ammonia  gas  returns  to  the  com- 
pressor. 

The  circuit  traversed  by  the  sweet  water  is  as  follows:  The 
exhaust  from  the  engine,  encountering  the  back-pressure  valve 
on  the  main  exhaust  pipe  from  the  engine,  is  diverted  through  a 
grease  separator  into  a  steam  condenser.  The  condensed  water 
then  passes  through  the  vacuum  reboiler  and  enters  the  suction 


Back 


Fig.  38- — Vacuum  Distilling  System 


of  pump  P,  which  discharges  it  into  the  hot-water  storage  tank; 
from  here  it  flows  through  a  regulating  valve  through  the  water 
cooler  and  into  the  cold-water  storage  tank,  from  whence  it  is 
drawn  to  fill  the  ice  cans  as  required.  The  water  for  the  plate 
plant  passes  first  through  the  water  filter  in  the  engine  room, 
through  the  water  forecooler  and  into  the  plate  tank.  Similarly, 
the  air  used  for  agitation  in  the  plate-ice  tank  is  discharged  by 
the  air  compressor  through  an  air-storage  tank  in  the  engine  room, 
through  the  water  forecooler  and  into  the  plate-ice  tank. 

VACUUM  DISTILLING  SYSTEM 

Fig.  38  represents  a  vacuum-distilling  system,  having  an  evap- 
orator which  provides  the  second  means  of  maintaining  the  full 


98    ELEMENTARY  MECHANICAL  REFRIGERATION 

capacity  of  the  ice  plant  when  the  available  sweet  water  is  insuffi- 
cient. For  simplicity  only  the  distilling  part  of  the  ice-making 
plant  is  shown  in  this  illustration. 

The  exhaust  steam,  as  before,  passes  first  through  a  grease 
separator,  but  in  this  case  it  also  passes  into  an  evaporator,  where 
the  steam  must  stop,  the  heat  being  carried  over  by  the  vapor  to 
the  steam  condenser.  Assuming  that  the  engine  is  running  under 
18  inches  of  vacuum,  the  exhaust  from  the  low-pressure  cylinder 
will  enter  the  evaporator  at  about  168°  Fahrenheit.  The  steam 
enters  the  dead-ended  copper  tubes  T,  which  extend  upward  at  a 
slight  angle  through  the  tube  sheet  into  compartment  S.  Here  it 
is  condensed  by  cooling  water  circulated  from  the  bottom  of  the 
evaporator,  through  the  centrifugal  pump,  distributing  pipe  L  and 
discharge  line  M.  On  the  condenser  side  of  the  tube  sheet  a 
vacuum  of  from  24  to  26  inches  is  maintained  by  the  condenser 
and  this  higher  vacuum  enables  the  heat  liberated  by  the  conden- 
sation of  every  1.15  pounds  of  exhaust  steam  to  evaporate  about 
one  pound  of  cooling  water.  The  cooling-water  vapors  are  lique- 
fied in  the  steam  condenser.  Here  they  are  joined  by  the  condensed 
exhaust  steam  from  the  evaporator,  which  is  drawn  through  pipe 
N  by  the  higher  vacuum  in  the  condenser,  and  also  by  a  small- 
amount  of  vapor  drawn  through  the  vent  pipe  from  the  top  of  the 
vacuum  reboiler,  condensed  water  from  both  the  evaporator  and 
steam  condenser  being  drawn  into  the  reboiler  by  the  vacuum 
maintained  in  the  steam  condenser.  The  water  from  the  steam 
condensed  in  the  coils  of  the  reboiler  drains  into  a  trap  provided 
with  a  float,  which  as  soon  as  the  water  has  collected  to  a  certain 
level,  admits  it  into  the  suction  line  leading  to  the  sweet-water 
pump  Q.  This  pump  discharges  the  sweet  water  into  a  hot-water 
storage  tank,  from  whence  it  flows  through  the  condensed-water 
cooler,  deodorizer  and  condensed-water  forecooler  to  the  ice  cans. 
In  the  reboiler  a  float  valve  controls  the  operation  of  the  condensed- 
water  pump,  allowing  it  to  draw  water  from  the  reboiler  only  when 
it  has  accumulated  to  a  predetermined  height.  In  the  trap  from 
which  the  water  condensed  in  the  coils  of  the  reboiler  is  drawn 
there  is  a  similar  float  valve,  opening  only  when  there  is  a  certain 
amount  of  water  present.  A  float  valve  in  the  hot-water  storage 
tank  controls  the  position  of  another  valve  through  which  water 
from  the  ammonia  condenser  pan  flows  into  a  regulating  device 
X,  which  operates  a  butterfly  valve  in  the  sweet-water  supply  line 


ICE-MAKING  SYSTEMS  99 

leading  to  the  ice  cans  and  prevents  the  drawing  of  water  from  the 
storage  tank  below  a  certain  level.  These  precautionary  measures 
are  all  taken  to  prevent  the  possibility  of  air  entering  the  pipes 
of  the  distilling  system. 

The  deodorizer,  into  which  the  sweet  water  is  introduced 
through  a  strainer  to  insure  uniform  distribution  through  the  filter 
bed,  consists  of  a  vertical  cylindrical  shell  filled  with  charcoal  cov- 
ered with  a  second  strainer  which  prevents  any  of  the  material 
from  floating  and  entering  the  discharge  pipe  at  the  top.  By  means 
of  a  simple  bypass  the  deodorizer  can  be  cut  out  of  the  system  for 
cleaning,  and  the  sweet  water  fed  direct  from  the  cooler  to  the 
cans.  In  some  instances  the  presence  of  iron  salts  in  the  water 
makes  it  advisable  to  supplement  the  deodorizer  with  a  sponge 
filter. 

The  forecooler  shown  in  the  illustration  consists  of  an  insulated 
compartment  in  which  a  direct-expansion  coil  is  installed  over  the 
distilled-water  coil.  Water  is  circulated  from  the  pan  beneath 
these  coils  and  passes  over  the  expansion  coil  where  it  is  cooled  to 
practically  32°;  it  then  gravitates  down  over  the  water  coil  and 
absorbs  heat  from  the  sweet  water.  As  the  circulating  liquid  is 
water,  it  is  impossible  to  freeze  up  the  sweet-water  coils,  and  since 
this  circulating  liquid  can  be  chilled  to  the  freezing  point  the  con- 
densed water  can  also  be  cooled  to  within  a  very  few  degrees  of 
the  freezing  point,  resulting  in  a  great  saving  in  freezing  time, 
which  is  equivalent  to  increasing  the  capacity  of  the  ice-freezing 
tanks.  The  reboiling  of  the  sweet  water  under  a  vacuum  at  a 
temperature  of  from  200°  to  204°  not  only  reduces  the  amount  of 
steam  required  to  effect  the  reboiling,  but  also  the  amount  of  cool- 
ing necessary  to  reduce  its  temperature  to  the  freezing  point. 


CHAPTER  VII 

THE  INSTALLATION  AND  OPERATION  OF  REFRIGER- 
ATING SYSTEMS 

INSTALLATION 

It  is  scarcely  necessary  to  state  that  every  detail  connected 
with  the  installation  of  the  piping  for  ammonia,  or  other  gases 
employed  as  a  working  medium,  should  be  executed  with  the 
greatest  care.  Only  such  materials  as  have  been  found  by  re- 
sponsible builders  to  be  well  adapted  to  their  respective  purposes 
should  be  employed.  For  ammonia,  good  full  weight  wrought- 
iron  pipe  is  to  be  recommended  for  the  expansion  or  low-pressure 
side,  and  extra  heavy  pipe  and  ammonia  fittings  of  approved  design 
for  piping  the  compression  side. 

In  damp  places,  where  the  low-pressure  gas  headers  are  liable 
to  rust  abnormally,  these  also  should  be  of  extra  heavy  pipe. 

Ammonia  pipe  joints  are  usually  made  up  with  lead  or  rubber 
gaskets  in  male  and  female  flanges,  sweated  on  the  pipes.  Some 
builders  employ  a  litharge  and  glycerin  cement  in  making  up 
screwed  joints  instead  of  solder,  and  there  is  little  difficulty  in 
making  such  joints  tight  if  scrupulous  care  is  exercised  in  seeing 
that  only  true,  sharp,  properly  formed  threads  are  used;  that  they 
are  thoroughly  cleaned,  for  which  purpose  gasolene  is  to  be  recom- 
mended; that  the  litharge  is  freshly  and  thoroughly  mixed  into 
a  thin  paste;  and  that  the  joints  are  made  up  tight. 

It  seems  trite  to  suggest  that  gasket  and  flange  joints  should  be 
drawn  up  squarely,  but  many  a  charge  of  ammonia  has  been  lost 
through  lack  of  attention  to  this  detail.  Rubber  gaskets  are  par- 
ticularly likely  to  blow  out  of  improperly  drawn  up  flanges  months 
later  when  the  rubber  has  become  softened  by  the  oil. 

When  the  erection  of  the  plant  is  complete,  and  the  piping 
thoroughly  blown  out  to  free  it  from  dirt,  scale,  metallic  chips  and 
other  foreign  substances,  an  air  pressure  of  not  less  than  300  pounds 
should  be  pumped  on  it  to  test  for  leaks. 

Leaks  resulting  from  split  pipes  and  improperly  made  up  gasket 
joints  may  be  readily  located  by  the  sound:  In  fact,  in  a  still 
cooler,  sound  is  the  most  efficient  means  of  detecting  very  small 


INSTALLATION  AND  OPERATION  101 

leaks,  especially  of  ammonia,  when  the  air  has  become  so  laden  with 
the  fumes  as  to  make  the  usual  methods  of  testing  difficult.  When 
all  of  the  leaks  have  apparently  been  stopped,  it  is  advisable  to 
pump  a  pressure  on  the  piping  and  let  it  stand  for  ten  or  twelve 
hours.  The  drop  in  pressure,  provided  there  is  no  appreciable 
change  in  temperature,  will  indicate  the  amount  of  leakage.  As  a 
final  precaution  the  air  may  be  allowed  to  escape  and  the  system 
again  charged  with  air  into  which  a  sufficient  amount  of  ammonia 
has  been  fed  to  make  any  leak  easily  detected  either  by  smell  or 
by  means  of  sulphur  sticks.*  The  approximate  location  having 
been  found  by  means  of  the  sulphur  fumes,  the  exact  position  of  the 
leak  may  be  located  by  oil  applied  to  the  leak  by  means  of  a  long- 
nosed  oil  can  or  soapsuds  applied  with  a  brush. 

Where  there  is  a  likelihood  of  existence  of  leaks  in  pipe  or  sub- 
merged condensers,  or  other  places  where  escaping  ammonia  would 
not  readily  be  detected  because  of  its  entering  into  solution  in  the 
cooling  water  or  cooled  brine  as  the  case  may  be,  it  is  advisable 
to  test  these  liquids  periodically  with  some  reliable  reagent. 
Where  there  are  not  too  many  foreign  substances  present,  the 
litmus  and  turmeric  papers  are  fairly  reliable.  A  more  satisfactory 
reagent,  however,  for  use  under  the  varied  operating  conditions 
of  refrigerating  and  ice-making  plants,  is  Nessler's  solution,  a  few 
drops  of  which  added  to  the  suspected  water  or  brine  will  show  a 
yellow  discoloration  for  slight  traces  of  ammonia,  increasing  with 
the  amount  of  ammonia  present  until  with  large  quantities  a 
reddish-brown  precipitate  is  formed.  ',,<  i  '•!  : 


REPAIRING    LEAKS 


Many  small  leaks  such  as  occur  in  ammonia  fittings  may  be 
stopped  by  the  judicious  use  of  a  set  of  small  calking  tools. 

Porous  spots  in  iron  and  steel  castings  may  sometimes  be 
remedied  by  the  judicious  use  of  some  rusting  solution  such  as  sal 
ammoniac  or  hydrochloric  acid.  Where  the  leaks  are  occasioned 

*  Sulphur  sticks  used  for  testing  for  ammonia  are  made  of  pieces  of 
white  pine,  or  other  wood  which  burns  with  little  smoke,  split  into  splinters 
half  the  size  of  a  lead  pencil  and  from  6  to  8  inches  long.  These  sticks  are  then 
dipped  into  molten  sulphur  so  that  about  4  inches  of  the  ends  are  thoroughly 
coated,  and  after  being  cooled  are  ready  for  use.  In  testing  for  leaks,  the 
sticks  are  ignited  and  held  close  to  the  suspected  pipe  or  fitting.  If  there  is 
escaping  ammonia,  it  will,  on  coming  in  contact  with  the  burning  sulphur, 
produce  a  very  noticeable  white  cloud. 


102  ELEMENTARY  MECHANICAL  REFRIGERATION 

by  blow  holes  of  considerable  size  occurring  where  the  application 
of  pressure  will  tend  to  drive  the  substance  into  the  porosities  of 
the  iron,  some  of  the  patented  rust-joint  preparations  may  be 
effective. 

Troublesome  leaks  due  to  imperfect  welds  in  the  seams  of 
pipes  may  be  effectively  repaired  by  first  cleaning  the  pipe  with 
a  file  and  some  suitable  soldering  solution,  then  applying  a  closely 
laid  course  of  bright  steel  wire.  The  layer  of  wire  should  then  be 
saturated  with  the  soldering  solution  and  the  whole  surface  thor- 
oughly coated  with  solder,  special  care  being  taken  to  see  that  it  is 
thoroughly  sweated  in  at  the  point  where  the  leak  occurs.  The 
steel  wire  supplies  the  tensile  strength,  the  lack  of  which  in  the 
solder  would  often  allow  the  ammonia  under  pressure  to  lift  off 
the  solder  coating.  A  hard  solder  should  be  employed  and  the 
steel  wire  should  be  thoroughly  "tinned"  to  protect  it  from  rust. 

For  soldering  iron  and  steel  pipes  two  soldering  solutions  should 
be  employed,  the  first  being  simply  a  cleaning  solution  of  con- 
centrated hydrochloric  acid,  and  the  second  a  saturated  solution 
of  zinc  chloride,  commonly  known  among  tinners  as  "cut  acid." 
This  second  solution  is  prepared  by  dissolving  metallic  zinc  in 
concentrated  hydrochloric  acid.  Some  builders  add  to  the  zinc 
chloride  thus  formed  an  equal  amount  of  ammonium  chloride. 

Leaks,  both  in  pipes  and  castings,  may  be  repaired  and  sepa- 
rate pieces  of  pipe  may  be  welded  together  to  form  continuous 
pipes,  coils  and  headers,  by  means  of  improved  processes  of  electric 
and  oxyaqe>ty:li-ne  welding.  Ammonia  receivers,  as  well  as  larger 
shells  such  as  are  uaed  for  constructing  absorbers,  condensers  and 
generators  of  absorption  machines,  are  also  made  by  this  process. 

CHARGING  A  REFRIGERATING  SYSTEM 

After  it  has  been  found  that  the  system  is  perfectly  tight,  the 
air  and  the  ammonia  should  be  allowed  to  escape,  after  which  the 
whole  system  should  be  pumped  down  to  a  vacuum. 

Even  pumping  a  vacuum  does  not  insure  the  expulsion  of  all 
the  air,  but  it  becomes  greatly  rarified  as  it  expands  under  the 
reduced  pressure  and  the  remainder  may  be  allowed  to  stay  in  the 
system  until  displaced  by  purging  at  the  condensers,  or  a  large 
percentage  of  it  can  be  driven  out  of  the  system  by  the  judicious 
manipulation  of  the  ammonia.  If,  for  example,  the  ammonia  be 
admitted  very  slowly  at  one  end  of  a  long  run  of  pipe,  it  will  drive 


INSTALLATION  AND  OPERATION  103 

the  air  before  it  without  mixing  with  it  to  any  great  extent,  and, 
if  at  the  other  end  of  the  pipe  line  a  valve  be  opened  or  a  flange 
union  be  cracked  after  sufficient  ammonia  has  been  admitted  to 
produce  a  pressure  above  that  of  the  atmosphere,  the  air  can  be 
allowed  to  escape  until  it  contains  too  large  a  percentage  of  am- 
monia, when  the  opening  is  closed. 

To  initially  charge  or  recharge  the  system,  connect  the  shipping 
drums  of  anhydrous  ammonia,  one  at  a  time  (or  more  if  the  plant 
is  of  large  capacity  or  the  initial  charge  is  being  put  in  and  one 
wishes  to  save  time)  to  the  charging  valve  usually  placed  between 
the  master  expansion  valve  on  the  liquid  line,  where  it  leaves 
the  receiver,  and  the  expansion  coils  or  brine  cooler.  This  connec- 
tion is  most  easily  made  by  a  special  fitting  built  up  with  two 
swing  joints,  one  end  threaded  to  fit  the  valves  on  the  shipping 
drums  and  the  other  provided  with  a  flanged  or  threaded  end  to 
connect  to  the  charging  valve.  When  the  connection  has  been 
made  the  air  in  the  pipe  may  be  expelled  by  slightly  opening 
either  the  charging  or  the  shipping-drum  valve  and  loosening 
the  flanged  swing  joint  nearest  the  opposite  end. 

The  connection  having  been  carefully  made,  the  main  valve 
on  the  receiver  is  closed  and  the  low-pressure  side  is  "pumped 
down"  by  allowing  the  compressor  to  continue  operation  after 
the  liquid  has  been  shut  off.  By  the  "pumping  down"  process 
the  ammonia  in  the  expansion  side  of  the  system  is  compressed 
and  discharged  into  the  compression  side  of  the  system,  where 
it  is  condensed  and  flows  to  the  liquid  receiver  which  it  may  fill 
as  well  as  the  lower  pipes  of  the  condenser. 

When  the  low-pressure  gauge  indicates  that  the  pressure  in 
the  expansion  coils  has  been  reduced  to  zero,  or  atmospheric, 
pressure,  the  charging  valve  may  be  opened  wide  and  then  the 
valve  on  the  shipping  drum  may  be  "cracked,"  allowing  a  small 
stream  of  the  liquid  to  pour  into  the  system.  The  valve  on  the 
drum  virtually  becomes  the  expansion  valve  of  the  system  and 
its  manipulation  should  be  governed  by  the  same  rules  that 
govern  the  other  expansion  valves  when  the  machine  is  in  normal 
operation,  except  that  it  is  better  not  to  carry  the  back  pressure 
quite  as  high  as  usual.  This  pressure  may  be  anything  above 
atmospheric,  but  there  is  an  advantage  in  not  reducing  the 
pressure  below  atmospheric  as  the  vacuum  would  tend  to  draw 
air  into  the  system  through  the  charging  connection  when  the 


104  ELEMENTARY  MECHANICAL  REFRIGERATION 

drum  is  disconnected  if  the  charging  valve  is  not  absolutely  tight, 
and  a  considerable  inrush  of  air  is  obviously  less  easily  detected 
than  a  very  slight  leak  of  ammonia  outward.  While  the  pro- 
duction of  a  lower  pressure  within  the  refrigerating  system,  than 
that  of  the  atmosphere  without,  undoubtedly  hastens  the  opera- 
tion of  charging,  there  is  always  the  tendency  to  draw  air  or  water 
into  the  system.  A  Vacuum  should,  accordingly,  never  be  pumped 
until  it  has  been  demonstrated  beyond  all  reasonable  doubt 
that  the  system  contains  no  leaks.  Small  leaks  into  the  system 
are  not  readily  detected,  and  it  is  evident  that  much  more  trouble 
can  be  made  by  what  water  a  small  leak  will  let  into  a  system 
thai*  by  the  amount  of  ammonia  the  same  leak  will  let  out. 

When  an  open  connection  is  made  between  the  shipping  drum 
and  the  system,  the  liquid  is  forced  out  of  the  drum  into  the  system 
by  the  pressure  of  the  gas  above  the  liquid  just  as  water  is  forced 
out  of  the  blowoff  of  a  boiler  by  the  steam  pressure  above  the 
water.  The  only  difference  is  that  it  requires  a  higher  tempera- 
ture than  that  of  the  atmosphere  in  the  engine  room  to  raise 
steam  pressure,  while  any  temperature  above  zero  will  give  a 
pressure  above  atmospheric  in  the  case  of  ammonia. 

This  is  made  mechanically  possible  by  the  construction  of 
the  shipping  drum  valve,  which,  after  passing  through  the  head, 
turns  down  to  within  about  half  an  inch  of  the  side  of  the  cylinder. 
When,  as  is  advisable,  the  opposite  end  of  the  drum  is  elevated 
a  few  inches,  there  remains  only  a  very  small  volume  of  the  drum 
below  the  level  of  the  outlet,  and  this  has  its  advantage  in  that 
heavier  impurities  tend  to  remain  in  the  drum  instead  of  passing 
into  the  system. 

That  the  liquid  ammonia  will  pass  from  the  shipping  drum  into 
the  system  without  the  necessity  of  pumping  is  evident.  If  the 
engine-room  temperature  be  80°  Fahrenheit,  for  example,  the 
pressure  in  the  drums  will  be  140  pounds  gauge,  or  there  will  be 
140  pounds  difference  in  pressure  between  the  ammonia  and  the 
atmosphere  to  cause  the  flow.  If  the  drums  are  exposed  to  the 
sun,  the  temperature  may  rise  much  higher  than  that  of  the  sur- 
rounding air  and  even  dangerous  pressures  may  result.  It  is 
accordingly  advisable  to  store  ammonia  drums  in  a  cool  place. 
The  shipping  drums  are  designed  to  carry  any  reasonable  pressures, 
but  there  is  a  remote  possibility  that  the  drum  may  be  filled  too 
full. 


INSTALLATION  AND  OPERATION  105 

In  this  case,  since  there  is  not  sufficient  vapor  space  to  take 
care  of  the  expansion  of  the  liquid  as  the  temperature  increases, 
and  since  liquids  are  practically  incompressible,  there  is  no  limit 
to  the  amount  of  pressure  that  may  be  produced  except  that  of  the 
ultimate  strength  of  the  drum.  There  is  the  same  danger  in  tightly 
closing  the  valves  on  all  the  outlets  to  the  liquid  receivers  when  it 
is  not  definitely  known  that  they  are  not  completely  filled  with 
liquid.  Explosions  due  to  such  causes  are  second  only  to  boiler 
explosions  in  their  disastrous  results. 

It  is  obvious  that  the  vapor  generated  in  the  drum  will  drive 
the  liquid  out  into  the  system  so  long  as  the  temperature  of  the 
liquid  is  such  as  to  produce  a  gas  pressure  higher  than  that  in*the 
system.  If,  for  example,  the  system  is  operating  under  15  pounds 
gauge  back  pressure,  16  pounds  vapor  pressure  in  the  drum  would 
suffice  to  expel  the  liquid.  The  temperature  of  the  liquid  corre- 
sponding to  a  pressure  of  16  pounds  is  about  0°  Fahrenheit.  From 
this  it  will  be  seen  that  the  only  disadvantage  of  charging  against 
back  pressure  is  that  the  liquid  will  not  flow  so  rapidly  into  the 
system  because  of  the  decreased  difference  in  pressure.  The  slight- 
est reduction  in  pressure  within  the  drum,  due  to  a  removal  of 
part  of  the  liquid,  causes  the  ammonia  to  boil  more  vigorously, 
generating  more  vapor  to  fill  the  increasing  space  above  the  liquid. 
The  temperature  at  which  the  liquid  boils  gradually  drops,  how- 
ever, until  at  a  pressure  of  about  47  pounds,  which  corresponds 
to  a  temperature  of  a  little  less  than  32°  Fahrenheit,  the  pipe  lead- 
ing from  the  drums  will  become  sufficiently  cold  to  precipitate  and 
congeal  atmospheric  moisture,  and  is  said  to  "  frost."  The  melt- 
ing of  this  frost  when  the  pressure  is  47  pounds  or  less  indicates 
that  there  is  no  more  ammonia  passing  through  the  pipe.  The 
valves  can  then  be  closed,  the  empty  drum  removed  and  a  full  drum 
connected. 

AMOUNT  OF  AMMONIA  CHARGE 

It  is  easier  to  form  an  opinion  as  to  the  amount  of  ammonia 
that  the  system  needs  while  it  is  operating  than  it  is  to  determine 
when  a  sufficient  amount  has  been  added.  Except  in  the  case  of 
initial  charges,  it  is  better  to  add  a  comparatively  small  amount 
of  ammonia  and  then  to  operate  the  system  for  a  sufficient  length  of 
time  to  restore  normal  conditions.  The  height  of  the  liquid  in  the 
gauge  glass  of  the  receiver,  or  the  general  performance  of  the 
plant  when  no  gauge  glasses  are  used,  will  give  the  engineer  an 


106  ELEMENTARY  MECHANICAL  REFRIGERATION 

idea  as  to  whether  or  not  more  ammonia  is  required.  It  should 
be  remembered  that  refrigeration  is  produced  by  the  absorption 
of  the  heat  required  to  change  the  liquid  ammonia  to  a  gas,  and 
since  it  takes  only  a  very  small  amount  of  heat  to  raise  the  tem- 
perature of  any  gas  that  passes  the  expansion  valve  in  company 
with  the  liquid,  little  cooling  effect  can  be  expected  from  the  gas. 

So  far  as  the  production  of  cold  is  concerned,  there  need  be 
only  sufficient  liquid  refrigerant  to  insure  a  solid  stream  at  the 
expansion  valves,  so  that  no  gas  may  enter  the  expansion  coils  at 
any  time.  The  passage  of  gas  can  be  readily  recognized  by  the 
intermittent  hissing  sound  produced  by  the  passage  of  quantities 
of  liquid  and  gas.  The  condition  in  which  there  is  just  enough 
liquid  to  give  a  solid  flow  at  the  expansion  valve  is  the  minimum 
charge  that  can  be  economically  employed.  A  lesser  quantity 
must  result  in  loss  of  both  capacity  and  efficiency. 

To  provide  for  unforseen  contingencies,  such  as  losses  of 
ammonia  through  leaks,  temporary  trapping  of  liquid  in  low  parts 
of  the  system,  etc.,  it  is  always  expedient  to  have  the  liquid  charge 
somewhat  in  excess  of  this  amount,  a  kind  of  credit  balance  in  the 
bank  to  guard  against  the  embarrassment  of  overdrawing  one's 
account  if  collections  do  not  come  in  from  the  expansion  coils, 
condensers,  etc.,  as  expected. 

Increasing  the  charge  of  anhydrous  ammonia  above  that  actu- 
ally required  to  insure  an  uninterrupted  flow  at  the  expansion 
valve,  will  work  no  harm  to  the  system  up  to  the  point  where  the 
liquid  fills  the  receiver  and  begins  to  encroach  upon  the  condensing 
surface.  To  be  sure,  the  more  liquid  lying  in  the  compression  side 
of  the  system  under  the  usual  conditions  of  operation,  the  less 
space  there  will  be  for  the  storing  of  additional  anhydrous  am- 
monia should  it  become  necessary  to  "pump  out"  the  low-pressure 
side.  The  additional  ammonia  occasions  an  additional  investment, 
but  in  the  majority  of  plants  it  is  expedient  to  carry  a  small  stock 
of  liquid  to  provide  for  contingencies;  and  aside  from  the  rather 
remote  possibility  of  an  accident  that  would  result  in  the  loss  of 
the  entire  charge,  it  is  better  to  have  the  ammonia  in  use  in  the 
system  than  lying  idle  in  shipping  cylinders. 

An  overcharge  of  ammonia  in  a  system  can  usually  be  detected 
in  two  different  ways.  Since  the  condensed  liquid  soon  becomes 
several  degrees  colder  than  the  uncondensed  gas,  the  parts  of  the 
compression  side  that  contain  liquid  ammonia,  whether  the  liquid 


INSTALLATION  AND  OPERATION 


107 


receiver  connecting  piping  or  pipes  of  the  condenser,  can  usually 
be  determined  by  their  lower  temperature.  Assuming  that  the 
plant  is  overcharged  to  such  an  extent  that  the  liquid  in  the  com- 
pression side  begins  to  fill  up  the  condenser,  thus  encroaching  on 
the  available  condenser  surface,  a  material  rise  in  head  pressure 
over  that  usually  observed  when  running  under  similar  conditions 
of  speed,  back  pressure  and  water  supply  with  only  sufficient 
liquid  in  the  system  to  insure  a  solid  flow  through  the  expansion 
valve,  would  be  expected.  As  it  is  usually  impossible  to  say 
whether  these  conditions  are'  exactly  constant  or  not,  a  slight 
increase  in  head  pressure  observed  on  increasing  the  charge  should 
not  be  accepted  as  proof  positive  that  the  system  has  been  over- 
charged, even  if  the  increased  pressure  seems  to  occur  under  con- 
stant conditions  of  operation. 

There  can  be  no  fixed  rule  by  which  to  determine  the  amount  of 
ammonia  required  for  a  direct-expansion  refrigerating  system. 
For  systems  not  including  sharp  freezers,  the  only  accurate  way 
is  to  calculate  the  amount  of  the  charge,  taking  as  a  starting  point 
the  amount  of  pipe  to  be  filled  with  the  refrigerant  in  both  the 
high-  and  the  low-pressure  sides  of  the  system.  The  following 
tables,  showing  cubical  contents  of  pipes  and  weights  of  gas  at 
different  pressures,  will  be  found  convenient  when  calculating  the 
amount  of  ammonia  required  to  charge  the  system. 

TABLE   IV.— RELATION   OF   CUBICAL   CONTENTS   TO   RUNNING   FEET 
IN   PIPES   OF   VARIOUS   SIZES 


Size  of  Pipe,  Inches 

Running  Foot  per  Cubic  Foot 
of  Contents 

Contents  in  Cubic  Feet  per 
100  Running  Feet 

t* 

1)1 
2 

270.00 
166.90 
96.25 
70.65 
42.36 

0.370 
0.599 
1.038 
1.415 
2.360 

TABLE   V.— WEIGHTS   OF  AMMONIA   VAPORS   AT   DIFFERENT 
GAUGE   PRESSURES 


Ammonia  Gauge 
Pressure 

Weight  of  1  Cubic 
Foot  of  Vapor,  Lb. 

Ammonia  Gauge 
Pressure 

Weight  of  1  Cubic 
Foot  of  Vapor,  Lb. 

0 
10 
20 
30 
40 
50 
60 
70 

0  .  0566 
0.0941 
0.1269 
0.1611 
0.1955 
0.2292 
0.2641 
0.2965 

80 
90 
100 
125 
150 
175 
200 

0  .  3304 
0.3617 
0.3939 
0.4766 
0.5566 
0.6340 
0.7188 

108  ELEMENTARY  MECHANICAL  REFRIGERATION 

The  number  of  hundreds  of  running  feet  of  pipe  in  the  system 
having  been  determined,  the  cubic  feet  contained  in  it  may  be 
found  from  Table  IV.  The  amount  of  ammonia  necessary  may  be 
ascertained  by  multiplying  the  cubical  contents  by  the  weight  of 
gas  per  cubic  foot  corresponding  to  the  pressure  to  be  carried  in 
the  pipes  when  the  system  is  in  operation.  The  weight  of  ammonia 
vapor  required  to  fill  both  high-  and  low-pressure  sides  of  the  sys- 
tem may  be  determined  in  this  way,  in  addition  to  which  a  liberal 
margin  should  be  allowed  for  reserve  liquid  in  the  receiver,  evap- 
orating liquid  in  the  expansion  coils  and  condensing  liquid  in  the 
condenser. 

Where  sharp  freezers  are  in  service,  a  much  larger  amount  of 
liquid  will  be  required  to  charge  the  low-pressure  side,  the  extra 
charge  increasing  very  rapidly  with  decreasing  pressures. 

When  the  refrigerating  machinery  is  to  be  operated  under  aver- 
age conditions,  an  ammonia  charge  figured  according  to  the  follow- 
ing tables  will  be  in  line  with  commercial  practice. 


TABLE   VI.— ANHYDROUS   AMMONIA   REQUIRED   FOR   THE   COMPRESSION 
SIDE    OF    REFRIGERATING    PLANTS 


Tons  of  Refrigeration 

Pounds  of  Ammonia 

Tons  of  Refrigeration 

Pounds  of  Ammonia 

5 

110 

75 

375 

10 

150 

100 

440 

15 

185 

150 

510 

20 

230 

175 

570 

25 

245 

200 

620 

30 

270 

225 

675 

35 

290 

250 

725 

40 

300 

300 

840 

45 

325 

400 

1040 

50 

350 

500 

1215 

TABLE   VII.— ANHYDROUS   AMMONIA    REQUIRED     PER    100   RUNNING   FEET 
OF   PIPE— EXPANSION   SIDE 


AMMONIA    FOR 
REFRIGERATING  PLANTS 
Direct  Expansion  and  Brine 
Cooling  Coils 

Size  of  Pipe 

AMMONIA  FOR  ICE  PLANTS 
Expansion  Coils  for  Can  and 
Plate  Use 

14  pounds 
18 
20 
25        " 

1  inch 
\l/i  inches 

1J4       " 

2 

8  pounds 
11 
12 
15 

In  ice  plants  the  amount  of  expansion  surface  per  ton  is  more 
nearly  a  constant  than  in  direct-expansion  refrigerating  plants. 
Since  different  sizes  of  expansion  piping  are  used  by  different 
builders,  the  expansion  surface  does  not  always  bear  a  fixed  rela- 


INSTALLATION  AND   OPERATION  109 

tion  to  the  space  to  be  filled  with  ammonia  vapor.  The  following 
ammonia  charges  for  ice-making  plants  may  be  considered  in  line 
with  average  practice. 

TABLE   VIII.— AMMONIA   REQUIRED   FOR   ICE -MAKING   PLANTS 

Tons  of  ice  per  24  hours 5  10  15  25  50  100 

Pounds  ammonia 100         250         500         1000         2000         4000 

The  amounts  given  in  Table  VIII  are  for  the  total  number  of 
pounds  required  to  charge  both  high-  and  low-pressure  sides  of  the 
ice-making  systems  in  question,  while  those  in  Table  VI  are  those 
required  for  the  compression  side  only. 

SALT 

The  amount  of  sodium  chloride  (NaCl)  required  to  make  brine 
for  an  ice  tank  of  given  capacity  is  also  subject  to  wide  variations 
on  account  of  the  diversity  of  designs  used  by  the  different  build- 
ers. The  factor  which  most  affects  the  amount  of  salt  necessary 
is  the  amount  of  space  left  between  the  bottoms  of  the  cans  and 
the  tank.  A  good  general  rule  is  to  allow  15  pounds  of  salt  per 
cubic  foot  of  brine  actually  required  to  fill  the  tank  when  the  cans 
are  in  place.  Another  rough  rule  is  to  allow  two-thirds  ton  of  salt 
per  ton  of  ice-making  capacity  of  tank  per  24  hours.  When  calcium 
chloride  (CaCl)  is  employed,  some  authorities  estimate  the  amount 
required  at  one  ton  CaCl  per  ton  of  ice-making  capacity. 


CHAPTER  VIII 


WORKING  PRESSURES 

It  has  already  been  pointed  out  that  a  given  substance  boils 
at  different  temperatures  under  different  pressures;  the  boiling 
point  being  raised  when  the  pressure  is  increased  and  lowered  when 
it  is  decreased.*  In  the  case  of  water,  for  example,  which  boils 
under  atmospheric  pressure  at  212°  Fahrenheit,  an  increase  in 
pressure  to  70  pounds  gauge  raises  the  boiling  point  to  316°  Fah- 
renheit, and  a  reduction  in  pressure  to  29.74  inches  vacuum  lowers 
it  to  32°  Fahrenheit,  or  to  its  freezing  point.  From  this,  since  the 
law  is  a  general  one  applying  to  all  known  liquefiable  gases,  it 
follows  that  to  produce  low  temperatures  the  pressure  on  the  re- 
frigerating medium  must  be  reduced  to  such  a  point  that  the  corre- 

*  A  common  and  very  simple  method  of  demonstrating  that  liquids  boil 
at  different  temperatures  as  the  pressure  varies  is  to  partly  fill  a  thin  glass 
flask  with  water.  Apply  heat  until  the  water  boils  vigorously,  cork  the  flask 
with  a  rubber  cork  thru  which  is  inserted  a  thermometer.  Immerse  the  flask 
in  a  vessel  of  cold  water.  The  condensation  of  the  steam  above  the  liquid  in 
the  flask  will  relieve  the  pressure  and  the  water  will  continue  to  boil  even 
though  at  a  temperature  several  degrees  below  212°.  The  air  having  been 
expelled  from  the  flask  by  the  steam  generated  before  the  flask  was  corked, 
the  removal  of  a  part  of  the  regular  atmospheric  pressure  of  15  pounds  per 
square  inch  previously  exerted  on  the  boiling  liquid  allows  the  vapor  to  pass 
off  more  easily,  hence  the  liquid  boils  at  a  lower  temperature. 

Besides  increasing  the  boiling  point  or  temperature  at  which  vapors  may 
separate  themselves  from  the  mother  liquid,  the  application  of  pressure  in- 
creases the  fusing  point  of  all  substances  that  contract  when  freezing.  In  both 
cases  the  pressure  resists  the  action  effected  by  the  application  of  heat,  and 
additional  heat  in  proportion  to  the  pressure  must  accordingly  be  applied  to 
overcome  the  resistance.  In  case  of  substances  that  contract  at  the  tempera- 
ture of  fusion,  such  as  ice,  the  application  of  pressure  assists  the  action.  Two 
pieces  of  ice  pressed  firmly  together  will  melt  at  the  point  of  contact  because 
of  the  assistance  that  pressure  lends  to  fusion.  Upon  the  removal  of  the  pres- 
sure, however,  the  pieces  will  freeze  firmly  together.  This  experiment  was  first 
performed  by  Sir  Humphrey  Davy  in  1799  as  a  means  of  disproving  the  then 
current  theory  that  heat  is  a  substance.  Davy's  experiment  was  made  in  a 
vacuum  at  a  temperature  below  the  normal  melting  temperature  of  ice.  Lord 
Kelvin  determined  that  the  freezing  point  of  water  is  lowered  .1235°  Fahr. 
for  each  atmosphere  (14.7  Ibs.)  increase  of  pressure. 


WORKING  PRESSURES  111 

spending  boiling  point  will  be  a  sufficient  number  of  degrees  below 
the  temperatures  to  be  produced  to  bring  about  the  heat  transfer 
through  the  expansion  coils  or  other  cooling  surfaces.  If,  for 
example,  it  is  desired  to  cool  a  cold-storage  compartment  to  10° 
Fahrenheit,  a  back  pressure  of  24  pounds  gauge  will  be  found  too 
high  to  allow  ammonia  to  boil  at  this  temperature.  At  23.64 
pounds  pressure  it  will  boil  at  exactly  10°  Fahrenheit,  but  since  this 
is  the  temperature  of  the  surrounding  air,  there  is  no  difference 
in  temperature  to  bring  about  a  heat  flow  and  the  boiling  will  not 
continue.  When  the  pressure  is  reduced  to  19.46  pounds  gauge, 
the  ammonia  will  boil  at  5°  Fahrenheit,  and  at  this  temperature 
there  will  be  sufficient  inflow  of  heat  from  the  10°  surrounding  air 
to  cause  quite  appreciable  refrigeration.  A  further  reduction  to 
15.67  pounds  gauge  lowers  the  temperature  of  the  boiling  ammonia 
to  0°  Fahrenheit  and  the  increase  in  temperature  difference  from 
5°  to  10°  Fahrenheit  will  effect  a  rate  of  heat  transfer  just  twice 
as  great  per  square  foot  of  pipe  surface  as  was  possible  with  half 
the  difference.  A  still  further  reduction  to  9.1  pounds  gauge  pres- 
sure will  allow  the  ammonia  to  boil  at  — 10°  Fahrenheit,  at  which 
temperature  the  heat  flow  from  the  10°  room  will  be  twice  as  great 
as  it  was  at  15.67  pounds  pressure  and  fouK.times  as  great  as  it  was 
at  19.46  pounds.  In  order  to  produce  the  same  amount  of  cooling 
effect  at  19.46  pounds  pressure  as  was  obtained  at  9.1  pounds  pres- 
sure, just  four  times  as  much  pipe  surface  would  have  to  be  em- 
ployed, and  in  order  to  do  as  much  as  at  15.67  pounds,  just  twice 
the  surface  would  be  required. 

If,  instead  of  direct  expansion,  brine  circulation  is  employed, 
it  will  be  evident  that  for  the  same  rate  of  heat  flow,  a  lower  pres- 
sure and  temperature  will  be  required  in  the  latter  case.  Assum- 
ing, for  example,  that  the  rate  of  heat  transmission  per  square  foot 
per  degree  difference  in  temperature  be  the  same  between  the  am- 
monia and  brine  and  between  the  brine  and  air  as  it  is  between 
the  ammonia  and  air  (an  assumption  which  is  not  wholly  accurate, 
but  which  will  simplify  the  example),  the  heat  transmission  be- 
tween the  ammonia  at  9.1  pounds  pressure  and  the  air  at  10° 
Fahrenheit  would  be  only  half  as  great  in  the  case  of  the  brine 
system  as  in  the  case  of  direct  expansion.  This  because  of  the 
fact  that  10°  difference  in  temperature  must  be  allowed  to  cause 
a  heat  flow  from  the  air  to  the  brine  and  another  10°  for  the  flow 
from  the  brine  to  the  ammonia.  On  this  basis,  in  order  to  pro- 


112  ELEMENTARY  MECHANICAL  REFRIGERATION 

duce  the  same  heat  flow,  9.1  pounds  back  pressure  would  have 
to  be  carried  in  the  case  of  brine  circulation  against  15.67  pounds 
in  the  case  of  direct  expansion.  The  relationships  are  expressed 
in  tabular  form  in  Table  IX. 

TABLE  IX.— BACK  PRESSURES  REQUIRED  TO  DOUBLE  DIFFERENCE 
IN  TEMPERATURE 


Back  Pressures  

23. 

64 

19.46 

15.67 

9.1  Ibs. 

Boiling  Temperatures  
Making  a  difference  in  temperature  between^ 
ammonia  and  brine  of  

10° 

F. 

5°F. 

0°F. 

-  10°F. 

10°F.;     brine  and  air    10°F. 

And  between  ammonia  and  air '  20°F. 

PRESSURE  AND  EFFICIENCY 

Where  the  piping  is  installed  and  cannot  be  increased,  there 
remains  only  one  of  the  two  variables.  To  increase  its  cooling 
capacity,  therefore,  lower  back  pressures  must  be  employed. 

The  saving  in  first  cost  by  the  installation  of  scanty  pipe  sur- 
face always  entails  correspondingly  lower  back  pressures,  and  is 
soon  lost  by  increased  operating  expense  due  to  decreased  effi- 
ciency. 

Where  there  is  only  one  temperature  to  be  produced  in  the  cold- 
storage  compartments,  a  back  pressure  is  usually  carried  such  that 
the  temperature  corresponding  to  that  pressure  will  be  from  10° 
or  less  on  low-temperature  work  to  30°  or  more  on  high-tempera- 
ture work,  below  that  of  the  " cooler"  temperature.  Under 
average  operating  conditions  the  cost  of  the  amount  of  expansion 
pipe  required  to  allow  this  range  in  temperatures  balances  up 
fairly  well  with  the  loss  in  efficiency  that  would  be  encountered 
if  less  expansion  piping  were  installed  and  a  lower  back  pressure 
carried.  The  lower  the  temperature  to  be  produced  the  lower 
the  efficiency  of  the  machine;  consequently  a  greater  expense 
will  be  warranted  in  pipe  area  so  as  to  increase  heat  transmission 
for  the  smaller  temperature  range. 

Where  several  different  temperatures  are  to  be  maintained 
with  one  back  pressure,  no  fixed  rule  can  be  followed  and  each 
individual  case  must  be  figured  out  separately.  If  only  a  small 
percentage  of  the  total  cooling  be  low-temperature  work,  it  is 
usually  advisable  to  increase  the  surface  and  to  reduce  the  tempera- 
ture range  between  the  liquid  ammonia  and  the  surrounding  air 
in  the  lowest  temperature  compartment.  In  this  case  the  use  of 


WORKING  PRESSURES 


113 


an  abnormal  amount  of  pipe  on  this  small  amount  of  low  tem- 
perature work  tends  to  increase  the  efficiency  of  the  whole  plant. 
While  the  nece'ssity  of  producing  a  low  temperature  in  a  single 
box  tends  to  reduce  the  efficiency  of  the  entire  plant,  or  that  part 
of  it  which  is  required  to  operate  at  a  low  back  pressure  because 
of  the  low  temperature,  there  is  a  slight  compensation  for  the 
decreased  efficiency  in  the  decreased  first  cost  of  expansion  piping 
for  the  higher  temperature  boxes.  The  reduced  ammonia  pres- 
sure occasions  a  correspondingly  reduced  ammonia  temperature. 
This  increases  the  range  in  temperature  between  the  ammonia  and 
the  outside  substance  to  be  cooled,  which  in  return  permits  a 
reduction  in  pipe  areas  in  proportion  to  the  increase  in  range. 


Back  Pressure,  Pounds  Absolute 


Fig.  39.  —  Curves  Showing  Properties  of  Various  Refrigerating  Media 
(Gauge  Pressures)  =  (Absolute  Pressures)  —  (15  Pounds) 

Some  idea  regarding  the  pressures  that  should  be  maintained 
in  expansion  coils  when  operating  the  different  kinds  of  refriger- 
ating media  may  be  gained  by  reference  to  the  curves  shown  in 
Fig.  39,  from  which  it  may  be  seen  that  for  an  expansion  tempera- 
ture of  0°  Fahrenheit,  such  as  would  ordinarily  be  employed  where 
temperatures  to  be  produced  are  from  10°  to  20°  Fahrenheit, 
expansion  pressures  for  these  different  refrigerating  media  are 
as  follows:  Ammonia,  30  pounds  absolute;  methyl  ether,  19 
pounds;  pictet  fluid,  14;  sulphur  dioxide,  10  pounds. 

While  no  definite  rules  can  be  laid  down  regarding  the  back 
pressures  that  should  be  carried  even  under  average  conditions, 
the  pressures  and  temperatures  given  in  Table  X  will  be  found  to 
be  fairly  accurate  for  ammonia. 


114  ELEMENTARY  MECHANICAL  REFRIGERATION 


TABLE   X.— BACK   PRESSURES   AND   TEMPERATURES    (AMMONIA) 


Temperature  of  room,  degrees  Fahrenheit 

5 

7 

10 
10 

15 
12 

20 
15 

28 
22 

32 
25 

36 

27 

40 
30 

50 
35 

60 

40 

Temperature  of  ammonia,  degrees  Fahr.  . 

-13 

-10 

-5 

0 

8 

12 

14 

17 

22 

26 

In  general,  the  engineer  should  endeavor  to  so  manipulate  his 
expansion  valves  as  to  carry  the  highest  back  pressure  possible 
and  still  produce  sufficient  refrigeration  in  his  coldest  coolers.  A 
second  limit  to  possibilities  in  this  direction  is  reached  when  no 
more  ammonia  feed  can  be  put  on  the  expansion  coils  without 
causing  liquid  ammonia  to  return  to  the  compressor,  causing  it  to 
pound  and  the  rod  stuffing  boxes  to  leak.  It  may  be  mentioned 
incidentally  that  the  back  pressure  can  be  carried  materially 
higher,  and  the  efficiency  of  the  plant  materially  increased,  by 
keeping  the  expansion  coils  free  from  the  insulating  effect  of  ice 
on  the  outside  and  oil  on  the  inside.  The  coating  of  ice  should 
be  kept  as  thin  as  possible  at  all  times  and  opportunity  should  be 
taken  to  remove  oil  from  the  expansion  coils  once  in  every  two 
or  three  seasons  at  most,  and  oftener  if  much  oil  is  thought  to  have 
worked  into  the  system. 

When  the  temperatures  get  too  low,  it  is  better  to  slow  down 
the  machine  rather  than  to  reduce  the  refrigerating  effect  of  the 
system  by  closing  down  expansion  valves,  reducing  the  back  pres- 
sure and  literally  throwing  away  power  because  the  refrigeration 
is  not  needed.  The  full  importance  of  this  truth  is  seldom  recog- 
nized by  either  the  supervising  or  operating  engineer,  and  it  is 
rarely  that  either  strives  for  the  last  pound  of  increased  back 
pressure  half  as  diligently  as  for  the  last  inch  of  vacuum  in  the 
steam  condensers,  although  the  former  pressure  is  of  far  more  im- 
portance than  the  latter  in  its  effect  on  the  general  efficiency  of  the 
plant. 

CONDENSER  PRESSURE 

Just  as  the  back  pressures  have  to  be  reduced  in  order  to  reduce 
the  boiling  point  of  the  refrigerating  medium  when  low  tempera- 
tures are  required,  the  condenser  pressure  always  rises  sufficiently 
to  raise  the  boiling  point  of  the  medium  when  the  temperature  of 
the  cooling  water  is  raised.  Table  XI  gives  the  approximate  con- 
denser pressures  that  should  result  from  the  use  of  different  quan- 
tities of  cooling  water  of  different  temperatures  on  condensers  of 
average  proportions. 


WORKING  PRESSURES 


115 


In  every  event  the  condenser  pressure  should  be  kept  as  low 
as  possible  and  the  back  pressure  as  high  as  the  temperatures  to 
be  produced  will  permit,  narrow  limits  between  such  pressures 

TABLE  XL— CONDENSER   PRESSURES  AND   TEMPERATURES    (AMMONIA) 


1  gallon  per  minute  per  ton  per  24  hours  — 
Temperature  of  cooling  water,  degrees  Fahr.  .  . 

60 
183 

65 
200 

70 
220 

75 
235 

80 
255 

85 
280 

90 
300 

Temperature  of  condensed  liquid  ammonia,  de- 

95 

100 

105 

110 

115 

120 

125 

2  gallons  per  minute  per  ton  per  24  hours  — 

130 

153 

168 

183 

200 

220 

235 

Temperature  of  condensed  liquid  ammonia,  de- 

77 

85 

90 

93 

100 

105 

110 

3  gallons  per  minute  per  ton  per  24  hours  — 

125 

140 

155 

170 

185 

200 

?15 

Temperature  of  condensed  liquid  ammonia,  de- 

75 

85 

90 

93 

95 

100 

105 

Ammonia  condenser  pressures  resulting  from  the  use  of  different  quantities  of  cooling 
water  at  different  temperatures. 

being  as  important  to  the  efficiency  of  a  refrigerating  system  as 
wide  ones  are  to  that  of  a  steam  engine,  in  which  the  economy  in- 
creases with  the  range  between  boiler  pressure  and  condenser 

pressure. 

FREEZING  BACK 

It  often  happens  that  the  expansion  valves  are  not  properly 
adjusted,  or  that  the  expansion  coils  are  so  arranged  that,  like 
poorly  designed  boilers,  there  is  abnormal  entrainment  and  con- 
siderable liquid  ammonia  is  carried  back  with  the  returning  vapor. 
In  this  case  the  scale  separator  may  act  as  a  veritable  separator 
and  temporarily  interrupt  the  passage  of  the  entrained  liquid. 
On  account  of  the  difficulty  of  returning  any  liquid  so  trapped 
to  the  expansion  coils  the  scale  traps  are  of  little  value  as  separators 
except  as  means  of  keeping  occasional  large  volumes  of  liquid 
from  returning  to  the  compressor.  Once  having  become  filled  with 
liquid  ammonia  they  remain  in  this  condition  for  some  time. 
Since  in  order  to  evaporate  the  ammonia  must  have  heat,  and 
since  the  temperature  of  the  boiling  ammonia  corresponding  to 
the  back  pressure  usually  carried  in  refrigerating  and  ice-making 
work  is  sufficiently  low  to  produce  ice  on  the  outside  of  the  traps, 
piping,  etc.,  these  parts  soon  become  heavily  insulated  with  ice 
which  further  materially  reduces  the  amount  of  heat  that  can  be 
absorbed,  and  the  entrained  liquid  enters  the  compressor  with  a 
considerable  capacity  for  absorbing  heat.  If  this  amount  is  abnor- 
mal it  may  cause  the  compressor  to  pound  for  the  same  obvious 
reason  that  a  steam  engine  pounds  when  it  receives  a  quantity  of 


116  ELEMENTARY  MECHANICAL  REFRIGERATION 

entrained  water  in  the  steam.  When  such  abnormal  quantities 
of  liquid  enter  the  compressor  cylinder,  it  is  usually  evidenced  by 
the  abnormal  cooling  effect  on  the  compressor  walls,  or  more 
noticeably  that  of  the  piston  rods  which  may  contract  sufficiently 
to  allow  the  ammonia  to  leak  by  the  packing.  The  evaporation 
of  this  entrained  liquid  ammonia  in  the  compressor  cylinder,  or 
that  introduced  directly  into  the  cylinder  through  an  expansion 
valve  designed  for  that  purpose,  refrigerates  the  gas  as  well  as 
the  compresssor  parts  and  tends  to  prevent  superheating  of  the 
gas  during  compression. 

The  evaporation  of  the  liquid  ammonia  remaining  in  the  expan- 
sion coils  when  the  compressor  is  shut  down  causes  the  rise  in 
back  pressure  usually  so  noticeable  a  few  hours  after  the  plant 
has  been  shut  down. 

CONDITION  OF  AMMONIA 

The  condition  of  the  ammonia  vapor  as  regards  saturation  or 
supersaturation  may  best  be  arrived  at  through  thermometers 
inserted  in  mercury  wells  in  the  return  and  discharge  lines  near  the 
compressor.  Tables  of  "properties  of  saturated  ammonia"  indi- 
cate at  a  glance  the  temperatures  at  which  the  vapors  should 
return  to  the  machine  under  different  conditions  of  back  pressure 
and  assumed  saturation. 

If  the  last  trace  of  the  liquid  ammonia  is  evaporated  before 
the  vapors  reach  the  compressor,  and  the  return  pipes  are  unin- 
sulated, there  is  likely  to  be  considerable  superheating,  i.e.,  the 
temperature  of  the  vapor  entering  the  compressor  is  likely  to  be 
several  degrees  higher  than  that  shown  by  the  tables  of  properties 
of  saturated  ammonia  gas  to  correspond  to  the  back  pressure 
carried.  This  condition  results  in  a  considerable  loss  of  efficiency 
and  should  not  be  allowed  to  continue. 

While  difference  in  opinion  regarding  the  amount  of  unevapo- 
rated  liquid  the  return  ammonia  gas  should  contain  in  order  to 
give  maximum  efficiency  has  given  rise  to  two  distinct  systems, 
viz.,  the  "wet"  and  the  "dry"  compression,  a  discussion  of  the 
relative  merits  of  the  two  systems  would  be  too  far-reaching  to 
warrant  its  introduction  here.  The  best  general  rule  regarding 
the  wet  or  dry  operation  of  compressors  is  to  follow  the  instructions 
of  the  respective  builders. 


WORKING  PRESSURES  117 

THE  FROST  LINE 

In  the  absence  of  more  accurate  means,  such  as  thermometers, 
for  determining  the  temperature  of  the  returning  ammonia  gas, 
the  "frost  line"  has  been  forced  into  service  to  give  at  least  some 
slight  indication  of  such  temperatures.  The  simple  formation  of 
frost  on  the  outside  of  a  pipe  containing  cold  ammonia  gas,  or,  in 
fact,  any  other  cold  medium,  indicates  nothing  more  nor  less,  how- 
ever, than  that  the  heat  from  the  outside  atmosphere  is  absorbed 
with  sufficient  rapidity  to  reduce  the  temperature  of  the  pipe  and 
nearby,  air  to  at  least  32°  Fahrenheit,  under  which  condition 
atmospheric  moisture  is  first  precipitated,  just  as  rain  or  dew  is 
formed  when  moisture-laden  air  becomes  cooled  by  heat  radiation 
to  air  at  a  lower  temperature  or  contact  with  other  colder  objects, 
and,  second,  is  frozen,  just  as  dew  is  frozen  to  form  frost  when  its 
temperature  is  reduced  below  32°  Fahrenheit. 

If  there  is  liquid  ammonia  enough  at  the  expansion  valve, 
frost  can  be  carried  the  full  length  of  a  coil  of  almost  any  length 
and  clear  back  to  the  machine,  if  desired,  at  a  back  pressure  of  25 
pounds,  because  the  temperature  of  saturated  gas  at  25  pounds 
pressure  is  11.5°  Fahrenheit,  which  is  20.5°  Fahrenheit  below  32°, 
the  freezing  point  of  water.  That  a  coil  does  not  frost  to  the  end 
under  a  back  pressure  of  25  pounds  indicates  that  either  there  is 
an  insufficient  supply  of  liquid  ammonia  at  the  expansion  valve 
or  that  there  is  an  obstruction  which  prevents  a  sufficient  amount 
from  passing  the  expansion  valve.  An  obstructed  expansion  valve 
is  indicated  by  there  being  little  or  no  change  in  the  sound  of  the 
passing  liquid  when  the  valve  is  opened  several  turns.  Such  ob- 
structions can  often  be  removed  by  the  sudden  opening  and  closing 
of  the  expansion  valve. 

Since  the  formation  of  frost  on  an  ammonia  pipe  is  influenced 
by  the  room  tempierature,  it  cannot  be  an  ideal  means  of  judging 
temperatures  within  the  pipes.  Where  considerable  entrained 
liquid  ammonia  is  present,  the  general  appearance  of  the  frost 
formed,  or  the  way  one's  wet  finger  sticks  to  the  pipe,  may  give 
some  slight  indication  of  the  action  taking  place  inside.  Where 
low  temperatures  are  carried,  the  return  gas  may  be  so  far  below 
32°  Fahrenheit  that  the  same  rise  in  temperature  that  would 
ordinarily  completely  change  the  appearance  of  the  return  line, 
if  it  took  place  at  a  higher  temperature,  would  not  affect  the  ap- 
pearance of  the  frost  line  at  all. 


118  ELEMENTARY  MECHANICAL  REFRIGERATION 

INSULATED  SUCTION  LINES 

It  may  be  generally  asserted  that  expenditure  of  energy  is  neces- 
sary to  remove  heat  from  any  substance  at  any  temperature  to  an- 
other substance  at  a  higher  temperature.  If,  then,  a  certain  amount 
of  the  heat  in  the  returning  ammonia  gas  has  its  origin  in  the  en- 
gine room,  where  its  absorption  is  manifested  by  frost  on  the  return 
line  to  the  compressor,  it  is  evident  that  additional  energy  will 
have  to  be  expended  in  the  engine  that  drives  the  compressor, 
which  energy  costs  coal,  labor  and,  finally,  money.  The  return 
lines  to  compressors  should  be  effectively  insulated  to  reduce  this 
loss.  Nothing  is  more  erroneous  than  the  argument  that  because 
the  returning  gas  has  passed  the  rooms  that  it  is  sent  out  to  cool, 
there  will  be  no  loss  because  of  the  heat  absorption  through  ex- 
posed, uncovered  cold  pipes.  The  useless  expenditure  of  a  single 
unit  of  refrigeration  is  just  as  prodigal  as  the  throwing  away  of  an 
equivalent  amount  of  money.  The  fact  that  such  losses  are  allowed 
to  continue  in  some  of  the  largest  refrigerating  and  ice-making 
plants  in  the  country  is  poor  excuse  for  their  existence  in  others. 


CHAPTER  IX 
CLEANING  THE  SYSTEM 

DEFROSTING  REFRIGERATOR  COILS 

The  problem  of  defrosting  cold  storage  coils  is  one  which  is  too 
often  ignored  at  the  time  of  making  the  installation.  Where  such 
has  been  the  case,  the  operator  often  finds  himself  working  at 
great  disadvantage,  not  only  because  of  his  inability  to  produce 
the  required  temperature,  but  also  because  of  the  decreased  effi- 
ciency of  the  mechanical  equipment  entailed  by  the  reduction  in 
back  pressures  necessary  to  coax  the  heat  from  the  cold-storage 
rooms  through  the  additional  resistance  offered  to  its  passage  by 
the  accumulated  ice.  This  disadvantage  affects  principally  the 
coal  bill  and  fortunately  for  the  operator,  though  unfortunately 
for  the  owner,  is  in  the  majority  of  cases  not  recognized,  or,  if 
apprehended,  is  not  charged  to  the  proper  account. 

The  effect  of  a  coating  of  ice  on  direct-expansion  pipes  may  be 
shown  as  follows:  Assuming  a  heat  transfer  of  10  B.t.u.,  in  round 
numbers,  per  hour,  per  square  foot  per  degree  of  difference  in 
temperature  inside  and  out,  for  a  flat  metallic  refrigerating  sur- 
face,* and  an  equal  amount  for  a  sheet  of  ice  one  inch  thick,  it 
follows  that  the  heat  transmission  through  a  square  foot  of  direct- 
expansion  cooling  surface  insulated  with  a  layer  of  ice  one  inch 
thick  will  be  only  one-half  that  of  the  uncoated  surface.  As  a 
matter  of  fact,  it  would  seem  from  the  context  that  the  value  of 
10  B.t.u.  given  as  the  heat  conductivity  of  ice  applies  to  plate-ice 
conditions  under  which  the  wetted  surface  of  the  submerged  ice 
will  transmit  materially  more  heat  than  a  dry  surface  in  contact 
with  air.  This  would  indicate  that  the  decrease  in  heat-trans- 
mitting capacity  of  direct-expansion  surfaces  in  air  due  to  a  coating 
of  ice  is  even  more  than  50  per  cent.  This  condition  will  be  par- 
tially offset  by  the  fact  that  on  account  of  the  increasing  diameter 
the  layer  of  ice  in  the  case  of  cylindrical  surfaces  such  as  pipes, 
which,  together  with  the  fact  that  such  coatings  usually  present 
an  irregular  surface,  further  increasing  the  heat-absorbing  area, 

*  See  Siebel's  "Compend  of  Mechanical  Refrigeration  and  Engineering," 
pages  190  and  207. 


120  ELEMENTARY  MECHANICAL  REFRIGERATION 

may  increase  the  heat  transmission  sufficiently  to  make  up  for 
the  lesser  heat  transfer  between  the  air  and  dry  ice  and  make  50 
per  cent  at  least  a  reasonable  estimate  of  the  loss  in  heat-absorbing 
capacity  due  to  one  inch  of  ice.* 

BRINE  COILS 

Brine  pipes  may  be  readily  defrosted  by  the  circulation  of  hot 
brine.  This  may  be  accomplished  through  the  main  feed  and 
return  headers  where  the  operation  does  not  have  to  be  performed 
very  frequently,  or  as  in  abattoirs  where  the  excessive  amounts 
of  moisture  from  the  hot  meats  to  be  chilled  make  the  accumulation 
of  frost  very  rapid,  or  by  a  separate  set  of  defrosting  headers. 


Fig.  40- — Diagram  of  System  for  Defrosting  Brine  Coils 

An  arrangement  such  as  is  illustrated  diagrammatically  in  Fig. 
40  allows  a  single  coil  to  be  defrosted  without  interfering  with  the 
operation  of  the  remaining  coils,  which  is  almost  an  absolute 
necessity  where  temperatures  are  to  be  kept  within  control  in 
abattoir  chill  rooms.  The  heating  of  the  brine  may  be  effected 
in  a  small  auxiliary  tank  by  the  exhaust  steam  from  the  pump 
used  for  circulating  the  hot  brine,  or  it  may  be  done  by  the  action 
of  a  small  steam  siphon. 

The  branches  of  the  main  supply  and  return  brine  headers  are 
provided  with  small  pipe  connections  on  the  coil  sides  of  the  coil 
supply  and  return  valves.  The  connections,  each  provided  with 
a  valve  or  stopcock,  communicate  into  small  supply  and  return 
headers,  the  former  connecting  with  the  discharge  side  of  the 
steam  siphon  and  the  latter  discharging  into  a  tank  or  barrel  into 

*  Under  average  commercial  conditions  of  intermittent  frosting  a  square 
foot  of  direct-expansion  surface  in  air  is  usually  credited  with  a  heat  transmis- 
sion of  only  from  2  to  4  B.t.u.  per  hour  per  degree  difference  in  temperature. 


CLEANING  THE  SYSTEM,  121 

which  the  siphon  suction  line  runs.  By  closing  the  main  sup- 
ply and  return  valves  on  any  one  or  any  number  of  the  coils  to 
be  defrosted,  and  opening  the  corresponding  valves  connect- 
ing with  the  defrosting  headers,  a  direct  circuit  is  established 
from  the  siphon  through  the  coil  and  back  to  the  barrel.  The 
admission  of  the  steam  to  the  siphon  starts  the  circulation  and 
at  the  same  time,  since  the  action  of  the  siphon  depends  on  the 
condensation  of  the  steam  in  the  brine  circulated,  the  brine  is 
gradually  heated.  That  this  heating  should  take  place  slowly  is  of 
importance  in  the  successful  defrosting  of  long  coils,  especially  in 
the  case  of  the  lock  seam  and  spiral  riveted  galvanized  iron  pipes 
that  have  been  so  commonly  used. 

DIRECT-EXPANSION  COILS 

In  the  case  of  direct-expansion  coils,  the  defrosting  method 
probably  most  satisfactory  where  the  cold-storage  temperatures 
are  above  32°  Fahrenheit  is  to  install  sufficient  coil  surface  to 
allow  a  part  of  the  coils  to  be  shut  off  at  any  time,  so  that  the  frost 
will  melt  without  artificial  heat  and  at  the  same  time  produce  a 
certain  amount  of  useful  refrigeration.  If  it  is  necessary  to  force 
the  defrosting  process  by  the  use  of  outside  heat,  a  hot  gas  line 
from  the  condenser  may  be  connected  to  the  liquid-line  connections 
to  the  separate  coils  just  inside  the  expansion  valves.  The  hot  gas, 
after  melting  the  ice  as  it  passes  through  the  coils,  returns  to  the 
compressor  together  with  the  return  gas  from  the  remaining  coils. 

Where  the  temperatures  carried  in  the  cold-storage  compart- 
ments are  below  32°  Fahrenheit,  and  in  which  the  defrosting  cannot 
be  effected  without  the  use  of  artificial  heat,  often  very  objection- 
able, two  methods  are  available,  viz. :  that  of  forcibly  removing 
the  ice  with  scrapers  and  that  of  suspending  over  the  pipes  trays 
of  calcium  chloride.  This  substance  is  exceedingly  deliquescent 
salt,  which  in  absorbing  moisture  from  the  air  forms  a  saturated 
calcium  brine  which  freezes  at  a  very  low  temperature.  In  trick- 
ling down  over  the  coils,  the  brine  melts  the  ice,  forming  a  more 
dilute  brine,  which  is  then  conducted  away  to  the  sewer,  or,  if  the 
quantities  involved  warrant  the  expenditure  of  labor,  may  be 
evaporated  and  the  calcium  chloride  recovered. 

OIL  IN  THE  REFRIGERATING  SYSTEM 

Next  to  unintelligent  design,  which  sometimes  provides  for  the 
operating  engineer  a  plant  that  cannot  be  made  to  develop  nearly 


122  ELEMENTARY  MECHANICAL  REFRIGERATION 

as  high  efficiency  as  operating  conditions  should  warrant,  and  un- 
intelligent operation,  which  fails  to  get  nearly  as  high  efficiency 
as  operating  conditions  and  mechanical  design  should  warrant, 
the  worst  foe  to  economy  is  foreign  matter  in  the  refrigerating 
system. 

In  order  that  the  oils  used  in  the  system  shall  not  stiffen  pro- 
hibitively at  the  low  temperatures  encountered  and  not  be  saponi- 
fied by  the  ammonia,  only  very  light  mineral  oils  can  be  employed. 
Such  oils  range  from  22°  to  30°  Baume,  corresponding  to  a  specific 
gravity  of  from  0.924  to  0.88.  These  oils  should  have  a  cold  test 
of  about  0°  Fahrenheit,  to  obtain  which  they  will  have  a  flash 
point  of  between  310°  and  400°  Fahrenheit.  This  low  flash  point 
implies  that  a  considerable  amount  of  vapor  will  be  given  off  at  a 
much  lower  temperature.  Since  discharge  temperatures  of  com- 
pression machines  often  approach  these  temperatures,  it  is  obvious 
that  a  considerable  amount  of  oil  will  pass  to  the  condenser,  not 
as  a  liquid  but  as  a  vapor.  Under  such  conditions,  since  there  is 
no  material  cooling  effect  in  the  oil  separator,  only  liquid  oil  would 
be  precipitated  at  that  point. 

Baffle  plates  on  which  the  discharged  gas  impinges  and  to 
which  particles  of  oil  will  tend  to  stick  by  adhesion  as  well  as  on 
account  of  the  abrupt  reversal  of  direction  of  flow  of  the  gas,  which 
tends  to  separate  out  the  slightly  denser  substances  by  centrifugal 
force,  are  precautions  in  the  right  direction;  but  except  when  dis- 
charge temperatures  are  low  it  is  useless  to  expect  to  intercept  all 
of  the  oil  until  it  has  been  actually  condensed.  This  operation 
being  carried  out  most  effectively  in  the  condenser,  the  oil  will 
pass  to  the  receiver  with  the  liquid  ammonia,  where,  since  there 
is  a  difference  in  specific  gravity  of  0.23  to  0.27,  the  separation  can 
be  more  easily  effected 

OIL  IN  COILS 

The  question  of  removing  oil  from  the  expansion  coils,  whether 
they  are  used  for  chilling  cold-storage  rooms,  for  chilling  brine  to  be 
circulated  through  cold-storage  rooms  or  for  chilling  the  brine  of 
an  ice  tank,  is  one  which  has  received  much  attention,  but,  al- 
though much  experimenting  has  been  done  and  a  few  patents  have 
been  issued,  no  cheap  and  effective  method  has  yet  been  devised. 
Where  coils  will  drain  so  that  there  will  be  no  danger  of  entrapping 
condensed  moisture,  the  most  effective  method  of  removing  the 
oil  is  to  pump  out  the  coils,  disconnect  them  and  blow  them  out 


CLEANING  THE  SYSTEM  123 

with  the  highest  pressure  live  steam  available,  letting  the  steam 
blow  through  each  coil  as  long  as  any  oil  appears  at  the  exhaust 
end.  The  brine  may  be  left  in  the  tank  and  heated  up  by  steam, 
so  as  to  prevent,  as  far  as  possible,  the  condensation  of  steam  in- 
side the  pipes,  or  if  the  brine  has  been  removed  the  same  result 
may  be  obtained  by  leaving  the  covers  on  the  tank  and  blowing 
in  live  steam. 

After  the  steam  has  been  blown  through  the  coils  until  no  more 
oil  appears,  each  coil  should  again  be  blown  out  with  air  to  remove 
any  traces  of  moisture  from  the  steam.  The  moisture-absorbing 
capacity  of  the  air  can  also  be  increased  by  heating  it  before  it  is 
introduced  into  the  coils.  The  coils  themselves  may  be  heated  as 
previously  described.  Long  coils  cannot  be  perfectly  cleaned  cold 
by  air  alone.  Where  coils  will  not  drain  in  the  tank  as  installed, 
the  only  effective  way  of  extracting  the  oil  is  to  remove  the  brine 
and  disconnect  them  at  such  points  as  will  enable  them  to  drain, 
or  remove  them  from  the  tank  entirely.  In  case  this  method  can- 
not be  employed,  ammonia  purifiers  may  be  installed  with  advan- 
tageous results.  These  purifiers  work  continuously  when  the 
plant  is  in  operation,  and  their  action  can  be  facilitated  by  fre- 
quently pumping  out  the  system.  While  it  can  hardly  be  expected 
that  all  of  the  oil  can  ever  be  removed  by  this  means,  their  slow 
continuous  action  is  of  great  benefit  in  plants  in  which  it  is  impossi- 
ble to  shut  down  in  order  to  employ  more  effective  methods,  and 
will  largely  prevent  the  accumulation  of  oil  in  new  or  recently 
cleaned  systems. 

PERMANENT  GASES 

The  action  of  so-called  permanent  gases  in  the  condenser  is 
less  detrimental  than  that  of  oil  in  the  expansion  coils  which  forms 
an  insulating  lining  of  fairly  high  efficiency  on  the  inside  of  the 
heat-absorbing  surfaces.  The  principal  effect  of  these  gases,  if 
their  operation  can  be  limited  to  the  condensers,  is  to  occupy  space 
that  should  be  available  for  the  ammonia  gas.  This  reduces  the 
effective  area  of  the  condenser  cooling  surface,  causing  an  in- 
creased head  pressure  with  the  usual  amount  of  cooling  water  or 
an  increased  amount  of  cooling  water  to  maintain  the  same  head 
pressure. 

These  so-called  permanent  gases  are  of  rather  uncertain  origin 
and,  as  the  name  implies,  are  gases  not  liquefiable  under  the  same 
conditions  of  temperature  and  pressure  as  ammonia.  In  a  new 


124  ELEMENTARY  MECHANICAL  REFRIGERATION 

plant  or  one  recently  overhauled  they  may  consist  almost  wholly 
of  atmospheric  air.  In  an  old  one  they  are  more  likely  to  consist 
of  nitrogen  and  hydrogen  from  decomposed  ammonia,  vapors  of 
oil  and  mixtures  of  other  hydrocarbon  gases  formed  by  the  action 
of  heat  on  hydrogen  in  the  presence  of  vapors  of  oil,  and  water  and 
other  impurities  contained  in  ammonia. 

There  is  a  considerable  difference  in  opinion  as  to  whether  or 
not  these  gases  are  heavier  or  lighter  than  ammonia,  and  accord- 
ingly whether  they  can  be  most  readily  purged  from  the  highest 
or  the  lowest  part  of  the  system.  It  seems  reasonable  to  suppose 
that  on  account  of  the  comparatively  rapid  flow  of  the  ammonia 
vapors  through  the  system,  that  sooner  or  later  these  gases,  wher- 
ever formed,  will  find  their  way  to  the  condenser.  If  the  liquid 
outlets  from  the  condenser  are  properly  sealed,  there  will  be  no 
other  way  for  them  to  escape  than  through  the  purge  valve  at  the 
top  of  the  condenser.  If  these  gases  are  lighter  than  ammonia, 
they  will  accumulate  at  the  top  of  the  condenser,  and  if  heavier 
they  will  be  driven  to  the  top  by  the  reexpanding  ammonia  in  the 
bottom  of  the  condenser  as  soon  as  the  pressure  is  removed  by  the 
opening  of  the  purge  valve. 

PUKGING 

Condensers  should  be  purged  as  often  as  the  accumulation  of 
gases  indicate  that  they  need  it.  To  do  this  most  advantageously, 
the  liquid  outlet  and  hot-gas  inlet  valves  of  the  coils  to  be  purged 
should  be  closed  and  a  liberal  supply  of  cooling  water  allowed  to 
flow  over  them  for  some  time.  The  permanent  gases  can  then  be 
purged  out  through  a  small  rubber  tube,  one  end  of  which  is  con- 
nected to  the  purge  valve ;  the  other  end  should  be  immersed  in  a 
pail  of  water.  If  permanent  gases  escape  when  the  purge  valve 
is  slowly  opened,  bubbles  will  rise  to  the  surface  of  the  water.  If 
only  ammonia  escapes,  the  bubbles  of  ammonia  gas  will  be  dis- 
solved in  the  water  before  reaching  the  surface,  giving  rise  to  a 
sharp  crackling  sound  such  as  that  caused  by  the  condensation 
of  steam  in  the  process  of  heating  water  by  the  direct  admission 
of  steam  through  an  open  pipe. 

When  the  water  in  the  pail  has  become  saturated  and  accord- 
ingly cannot  absorb  more  ammonia,  the  bubbles  will  rise  to  the 
surface  and  it  is  difficult  to  discriminate  between  ammonia  and  the 
other  gases.  For  this  reason  it  is  advisable  to  replace  the  aqua 


CLEANING  THE  SYSTEM  125 

ammonia  formed  by  fresh  water  often  enough  so  that  it  will  not 
become  saturated. 

This  requires  that  in  addition  to  keeping  the  inside  of  the 
condensers  free  from  obstructing  gases,  economy  of  power  and 
cooling  water  further  require  that  the  outside  of  the  condensers 
be  kept  as  free  as  possible  from  incrustations  left  behind  by  the 
cooling  water.  Scale,  like  ice  on  the  outside  and  oil  on  the  inside 
of  the  expansion  coils,  has  the  effect  of  insulating  the  heat  trans- 
mitting surfaces,  causing  either  higher  condenser  pressure  or  re- 
quiring the  use  of  an  excessive  amount  of  cooling  water. 

INCRUSTATION  ON  CONDENSER  COILS 

While  the  comparatively  high  working  temperature  of  conden- 
ser coils,  together  with  the  usually  ample  provisions  for  draining 
each  separate  coil,  prevents  the  accumulation  of  such  large  quan- 
tities of  oil  as  are  often  lodged  in  expansion  coils,  condenser  coils 
are  exposed  to  another  source  of  loss  of  efficiency  from  without. 
Where  the  available  cooling  water  is  abnormally  hard,  or  carries 
a  large  amount  of  suspended  matter,  ammonia  condensers,  and 
especially  steam  condensers,  soon  become  coated  with  a  deposit 
of  scale  or  mud,  which,  if  not  properly  removed,  becomes  a  more 
or  less  effective  insulator  according  to  the  composition  of  the 
deposit.  The  heat  conductivity  of  metallic  surfaces  is  not  the 
same  per  degree  difference  in  temperature  at  medium  and  low  as  it 
is  for  high  temperatures,  and  it  does  not  therefore  follow  that  the 
resistance  offered  by  the  scale  accumulating  on  the  outside  of 
atmospheric  and  submerged  ammonia  and  steam  condensers  is  the 
same  as  that  of  scale  on  the  inside  of  a  boiler.  However,  some 
slight  idea  of  the  extent  of  the  loss  may  be  gained  from  the  fact 
that  in  steam-boiler  practice,  the  insulating  effect  of  scale  results 
in  a  thermal  loss  corresponding  to  about  2  per  cent  of  the  fuel  for 
each  1-64  inch  in  thickness  of  scale. 

It  seems  superfluous  to  state  that  the  heat-absorbing  surfaces 
of  brine-cooling  coils  and  the  heat-radiating  surfaces  of  condenser 
coils  should  always  be  kept  covered  with  brine  and  condenser 
water  respectively.  Nevertheless,  it  is  not  uncommon  to  see 
refrigerating  plants  operating  with  the  brine  so  low  in  the  tanks 
that  the  top  expansion  coils  are  exposed  and  the  distribution  of 
water  over  the  condensers  so  irregular  that  a  large  portion  of  the 
surface  is  dry. 


CHAPTER  X 

CAPACITY  OF  REFRIGERATING  MACHINES 

In  general  there  are  two  methods  by  which  to  determine  the 
amount  of  cooling  effect  produced  by  a  refrigerating  machine. 

EFFECT  ON  SECONDARY  REFRIGERATING  MEDIUMS 

The  first  method  is  to  measure  the  results  produced  as,  for 
example,  the  cooling  effect  in  degrees  produced  on  a  known  quan- 
tity of  brine  or  other  mediums  having  known  specific  heats.  The 
number  of  units  of  heat  extracted  per  minute,  hour  or  day  being 
known,  the  capacity  of  the  machine  in  pounds  or  tons  of  equivalent 
ice-melting  capacity  may  be  readily  computed  by  dividing  the 
number  of  units  of  heat  extracted  by  the  number  of  such  units 
required  in  the  same  length  of  time  to  produce  refrigeration  at  the 
rate  of  one  ton  per  24  hours. 

EFFECT  ON  PRIMARY  REFRIGERATING  MEDIUMS 

The  second  method  is  to  actually  weigh  or  compute  the  number 
of  pounds  of  the  primary  refrigerating  fluid,  assumed  in  this  case 
to  be  ammonia,  passing  through  the  cycle  of  operations  per  unit 
of  time  and,  by  knowledge  of  the  amount  of  refrigerating  effect 
that  a  pound  of  the  refrigerating  fluid  is  capable  of  producing  under 
the  observed  conditions  of  back  pressure  and  liquid  temperature,* 
finally  arrive  at  a  more  or  less  accurate  estimate  of  the  amount  of 
cooling  effect  being  produced. 

UNITS 

The  units  involved  in  making  such  calculations  are  as  follows : 

(1)  British  Thermal  Unit  (B.t.u.). — Equivalent  to  the  specific 
heat  of  water,  or  the  amount  of  heat  required  to  raise  the  tempera- 
ture of  a  pound  of  water  through  1°  Fahrenheit  at  its  temperature 
of  maximum  density,  39°  Fahrenheit. 

(2)  Pound  of  Refrigeration. — Equivalent  to  the  expenditure  of 
negative  heat  (absorption  of  heat)  at  the  rate  of  144  B.t.u.  per 

*  On  account  of  the  usual  inaccuracy  of  pressure  gauges,  accurate  determi- 
nations of  liquid  temperatures  can  best  be  made  by  means  of  thermometers  set 
in  mercury  wells  inserted  in  the  liquid  lines  just  before  they  enter  the  expan- 
sion valves. 


CAPACITY  OF  REFRIGERATING  MACHINES     127 

twenty-four  hours;  144  B.t.u.  being  the  latent  heat  of  ice,  or  the 
amount  of  heat  required  to  melt  a  pound  of  ice  "from  and  at"  32° 
Fahrenheit  (ice  at  32°  melting  into  water  at  the  same  tempera- 
ture). 

(3)  Ton  of  Refrigeration. — Equivalent  to  the  expenditure  of 
negative  heat  (absorption  of  heat)  at  the  rate  of  2,000X144  B.t.u., 
or  288,000  B.t.u.  per  twenty-four  hours;  288,000  B.t.u.  being  the 
amount  of  heat  required  to  melt  a  ton  of  ice  "from  and  at"  32° 
Fahrenheit. 

From  the  foregoing  it  is  apparent  that  the  capacity  of  a  refrig- 
erant, which  extracts  heat  at  the  rate  of  288,000  B.t.u.  per  twenty- 
four  hours,  is  one  ton.  The  above  rate  is  equivalent  to  288, 000 -r- 
24  =  12,000  B.t.u.  per  hour,  or  288,000 -f-  (24X60)  =200  B.t.u.  per 
minute. 

To  absorb  heat  at  this  rate  certain  definite  quantities  of  the 
primary  refrigerating  fluid  must  be  evaporated  per  minute,  hour 
or  day;  in  addition  to  which  if  a  secondary  refrigerating  medium, 
such  as  brine,  is  employed,  a  certain  quantity  must  be  cooled 
through  a  sufficient  range  of  temperature  to  supply  the  amount  of 
heat  required  to  evaporate  the  primary  fluid. 

STANDARD  CONDITIONS 

It  has  been  proposed  to  employ  as  standard  185  pounds  head 
pressure — under  which  pressure  condensed  anhydrous  ammonia 
leaves  the  condenser  at  about  90°  Fahrenheit — and  15.67  pounds 
back  pressure,  corresponding  to  an  evaporating  temperature  in 
the  cooler  of  0°  Fahrenheit.  Under  these  standard  conditions, 
where  the  anhydrous  ammonia  enters  the  refrigerator  at  90° 
Fahrenheit  and  evaporates  at  0°  Fahrenheit,  from  27  to  28  pounds 
of  liquid  must  be  evaporated  per  hour  per  ton  of  refrigerating 
effect  produced.  This  means  that  the  ammonia  compressor  must 
have  an  effective  displacement  capacity  of  about  four  cubic  feet 
per  minute  per  ton. 

EFFECT  OF  PRESSURE 

The  refrigerating  capacity  of  evaporating  refrigerants  does  not 
depend  on  the  volume  of  gas  evolved,  except  as  volume  depends  on 
weight.  The  volume  of  gas  varies  widely  with  the  pressure,  but 
aside  from  the  cooling  effect  that  must  be  expended  on  the  liquid 
to  cool  it  from  the  condenser  temperature  down  to  the  cooler  tem- 
perature, the  weight  of  refrigerant  per  unit  of  cooling  capacity 


128  ELEMENTARY  MECHANICAL  REFRIGERATION 

produced  is  practically  constant  under  all  conditions  of  tempera- 
ture and  pressure.* 

At  10  pounds  back  pressure,  for  example,  corresponding  to  an 
evaporating  temperature  of  about  8°  below  zero,  the  volume  of  am- 
monia gas  is  10.8  cubic  feet  per  pound.  At  32  pounds  back  pres- 
sure, corresponding  to  an  evaporating  temperature  of  about  19°, 
the  volume  is  about  6  cubic  feet.  This  means  that  operating  at 
10  pounds  back  pressure  a  compressor  must  pass  approximately 
66  per  cent  more  volume  of  gas  per  unit  of  capacity  than  when 
operating  at  32  pounds  pressure. 

COMPUTED  CAPACITY — EXAMPLE 

The  method  of  arriving  at  the  size  of  the  compressor  required 
for  the  performance  of  a  given  refrigerating  duty  per  twenty-four 
hours  is  as  follows:  The  latent  heat,  or  the  amount  of  heat  ex- 
pressed in  B.t.u.,  required  to  evaporate  a  pound  of  anhydrous 
ammonia  at  10  pounds  back  pressure  is  about  560.  If,  for  example, 
150  pounds  condenser  pressure  is  carried,  the  liquid  ammonia  will 
pass  to  the  refrigerator  at  about  84  degrees.  The  evaporating 
temperature  corresponding  to  10  pounds  back  pressure  is  —8°, 
making  a  difference  of  temperature  of  92°  through  which  the  liquid 
must  be  cooled  before  it  can  produce  any  useful  cooling  effect  in 
the  refrigerator.  For  approximations,  the  specific  heat  of  the 
ammonia  liquid  may  be  taken  to  be  the  same  as  that  of  water, 
i.e.,  unity,  in  which  case  the  expenditure  of  92  B.t.u.  will  be  neces- 
sary to  cool  the  liquid  from  the  temperature  of  the  condenser  to 
that  of  the  refrigerator.  Subtracting  this  amount  from  the  latent 
heat — 560  B.t.u. — we  have  468  B.t.u.  remaining  for  the  perform- 
ance of  useful  work  in  the  refrigerator. 

POUNDS  REFRIGERATION 

The  latent  heat  of  ice,  taken  as  the  unit  pound  capacity  of 
refrigeration,  is  144.  The  evaporation  of  one  pound  of  anhydrous 
ammonia  under  the  foregoing  conditions  will  produce  468  -j- 144  = 
3.25  pounds  of  refrigeration;  this  regardless  of  the  time  in  which 
the  evaporation  takes  place. 

POUNDS  OF  AMMONIA 
The  evaporation  of  one  pound  of  anhydrous  ammonia  per  min- 

*This  presupposes  only  limited  superheating   when   the   refrigerant   in 
question  is  in  the  gaseous  state. 


CAPACITY  OF  REFRIGERATING  MACHINES     129 

ute  under  these  conditions  would  produce  refrigeration  at  the  rate 
of  468-^200  =  2.34  tons  per  twenty-four  hours.  At  the  rate  of 
one  pound  per  hour  the  tonnage  rate  per  twenty-four  hours  would 
be  468  -H  12,000  =  0.039. 

CUBIC  FEET  OF  AMMONIA 

At  10  pounds  back  pressure  each  pound  of  anhydrous  ammonia 
evaporated  has  a  volume  of  about  10.8  cubic  feet.  A  compressor 
displacing  this  volume  of  gas  per  minute  will  have  a  capacity  of 
2.34  tons,  or  a  ton  capacity  for  every  10.8^-2.34  =  4.6  cubic  feet 
of  piston  displacement  per  minute.* 

CAPACITY  OF  COMPRESSOR 

The  method  of  computing  the  capacity  of  a  refrigerating  ma- 
chine of  a  given  size  when  operating  at  a  given  number  of  revolu- 
tions, from  the  apparent  displacement  in  cubic  feet  per  minute, 
involves  two  other  very  important  factors:  First,  the  back  pres- 
sure at  which  the  compressor  is  operated;  second,  the  displacement 
efficiency  of  the  particular  compressor  in  question  when  operating 
at  the  back  pressure  in  question. 

The  amount  of  refrigeration  produced  is  directly  dependent 
on  the  number  of  pounds  of  the  refrigerating  fluid  evaporated,  due 
allowance  being  made  for  the  range  of  temperature  through  which 
the  liquid  must  be  cooled  before  it  can  do  useful  work  in  the  refrig- 
erator, and  the  cooling  effect  available  from  superheating  of  the  gas. 
DISPLACEMENT  EFFICIENCY  OF  COMPRESSOR 

When  the  compressor  itself  is  employed  as  a  meter,  i.e.,  when 
the  amount  of  the  refrigerating  medium  is  computed  from  the 
number  of  cubic  feet  of  volume  swept  out  per  minute  by  the  piston, 
it  is  necessary  to  assume  or  determine  the  compressor  displacement 
efficiency  in  order  to  arrive  at  the  actual  displacement  from  the 
apparent  displacement  indicated  by  the  volume  swept  out.  The 
weight  of  a  refrigerating  medium  vapor  is  directly  proportional 
to  its  absolute  pressure.  For  a  given  back  pressure  the  weight  of 
the  gas  per  cubic  foot  can  be  determined  directly  from  published 
tables  of  the  properties  of  the  refrigerating  medium  in  question. 

*  According  to  the  standards  adopted  by  the  Ice  Machine  Builders  in  1903, 
the  evaporation  of  27.7  pounds  of  ammonia  under  the  "standard"  conditions 
of  185  pounds  head  pressure  (90°  Fahrenheit)  and  15.67  pounds  back  pressure 
(0°  Fahrenheit)  constituted  a  ton  capacity.  On  this  basis,  approximately  5 
cubic  feet  of  displacement  would  be  allowed  per  ton  per  twenty-four  hours, 
in  a  compressor  of  80  per  cent,  displacement  efficiency. 


130  ELEMENTARY  MECHANICAL  REFRIGERATION 

The  displacement  efficiency  of  compressors,  or  the  ratio  of 
their  apparent  to  their  actual  cubical  displacement,  is  not  easy  to 
determine,  and  it  is  the  exception  rather  than  the  rule  that  the 
builders  of  compressors  can  themselves  give  the  efficiency  of  their 
various  machines  when  operated  under  different  heads  and  back 
pressures.  As  a  matter  of  fact,  the  only  exact  means  of  determining 
such  efficiencies  is  by  the  laborious  method  of  checking  the  amount 
of  refrigerating  fluid  apparently  passed  through  the  compressor, 
with  the  amount,  determined  by  weight,  actually  passed  through 
the  expansion  valve.  Even  this  method  has  a  serious  shortcoming 
in  the  case  of  "wet"  compression  machines  in  that  a  considerable 
amount  of  unevaporated  liquid  may  pass  through  the  compressor 
and  this  liquid  appearing  in  the  weights  of  liquid  passed  through 
the  expansion  valve  indicates  a  higher  displacement  efficiency 
than  the  compressor  deserves. 

APPARENT  CUBICAL  DISPLACEMENT 

To  compute  the  refrigerating  capacity  of  an  ammonia  com- 
pressor of  the  assumed  cylinder  dimensions  of  19x38  operating  at 
45  revolutions  per  minute  under  the  above  suggested  standard 
conditions  of  185  pounds  head  and  15.67  pounds  back  pressure: 
If  r  =  radius,  or  one-half  cylinder  diameter, 
1  =  length  of  stroke,  both  in  inches, 
n  —  number  of  revolutions  per  minute. 
Then  A  =  area  of  a  19-inch  piston  = 

[1]  A  =  n  r2  or  3.1416  X9.5  X9.5  =  283.53  sq.  in; 
V  =  volume  of  19x38-inch  cylinder. 
7trzl    283.53X38 


D  =  apparent  displacement  per  minute  double-acting 
compressor. 

[3]  D  =  2  ^-^  =  2X6.235X45  =  561.  15  cu.  ft. 
1728 

Somewhat  simplified  this  expression  becomes 
[4]  D  =  d2  1  n  0.00090903;  or,  since 

In     2ln 
—  =  -  =  piston  speed  P  S  in  feet  per  minute. 

[5]  D  =  d*PS  0.00545418  and  19X19x885X0.00545418  = 
561.15  cu.  ft. 


CAPACITY  OF  REFRIGERATING  MACHINES    131 

EFFECT  OF  WORKING  PRESSURES 

The  amount  of  heat  absorbed  in  the  evaporation  of  any  liquid 
depends  on  the  temperature  of  the  liquid  supplied  and  the 
pressure  under  which  it  evaporated  as  well  as  on  the  latent  heat 
of  vaporization  of  the  liquid.  Water,  for  example,  fed  to  a 
boiler  at  a  temperature  below  that  of  the  steam  generated  must  be 
heated  up  to  the  boiling  point  before  it  can  be  evaporated.  Liquid 
ammonia  fed  into  expansion  coils  at  a  temperature  above  that  of 
the  ammonia  vapors  must  similarly  be  cooled  down  to  the  boiling 
point  corresponding  to  the  pressure.  Since  the  only  means  of 
cooling  the  latter  is  by  its  own  evaporation,  it  is  evident  that 
just  so  much  liquid  as  evaporates  in  cooling  itself  can  do  no 
useful  refrigerating  work  on  other  products.  The  greater  the 
range  in  temperature  through  which  it  must  be  cooled,  whether 
on  account  of  the  abnormally  high  liquid  temperature  or  low 
evaporating  temperature,  the  less  will  be  the  useful  cooling  effect 
available  per  pound  of  refrigerant. 

The  total  heat  absorbing  capacity,  R  b  p  of  a  pound  of  liquid 
refrigerant,  is  known  as  its  latent  heat  of  vaporization  R.  And  its 
value  depends  on  the  back  pressure  b  p  at  which  it  evaporates. 
The  amount  of  heat  Q  that  must  be  extracted  to  cool  a  pound  of 
liquid  refrigerant  from  the  temperature  corresponding  to  the  head 
pressure  h  p  down  to  that  of  the  back  pressure  b  pis  the  difference 
between  the  values  of  the  "heat  of  the  liquid"  Q  under  the  two 
conditions.  The  available  cooling  effect  C  per  pound  of  refrigerant 
is  accordingly 


[61 


As  tables  of  the  properties  of  refrigerating  mediums  do  not  always 
give  values  for  the  "heat  of  the  liquid"  at  different  temperatures, 
the  number  of  heat  units  required  to  cool  the  liquid  may  be  arrived 
at  by  multiplying  the  number  of  degrees  (^-^2)  through  which 
the  liquid  is  cooled  by  S,  the  specific  heat  of  the  liquid,  and 
expression  [6]  becomes  [7],  in  which  have  also  been  substituted 
values  corresponding  to  standard  conditions. 


f*l 

Rbp 

— 

Qhp 

[       Qbp 

~ 

Available 

Latent  heat 

Heat  of  the 

IHeat  of  the 

Cooling  ef-  \  = 

of  vaporiza- 

•  — 

•j  liquid  under 

—  j  liquid  under 

• 

feet  per          1  tion  at  back 

head  pres- 

1   back  pres- 

pound     J       [pressure  b  p. 

-  I        sure 

l        sure 

- 

132  ELEMENTARY  MECHANICAL  REFRIGERATION 


Since  the  displacement  of  ammonia  compressors  is  expressed 
in  cubic  feet,  the  available  cooling  effect  per  cubic  foot  of  gaseous 


17] 


B.T.U.  PER  CUBIC  FOOT 

refrigerant  passing  through  the  compressor  is  most  frequently  em- 
ployed.    This  may  be  readily  determined  by  dividing  the  expres- 
sion [7]  by  V,  the  volume  occupied  by  a  pound  of  ammonia  under 
back  pressure  b  p  and  for  standard  conditions  becomes 
RbpXS  (ti-t*)     555.5-1  (90-0) 


fl&p 

^     i     r     t2 

f      c      i 

Latent 

S 

Temper- 

temper- 

o 

Available 

heat  of 

Specific 

ature 

ature 

cooling       _ 
effect    per  j 
pound  — 

evapo- 
ration at 
back 

-- 

heat 
taken  as  • 

unity 

.,. 

corre- 
sponding 
to  head 



corre- 
sponding 
to  back 

r 
46^  *» 

pressure 

* 

pressure 

pressure 

T±U«J  •  «J 

(15.67) 

1       J 

hp 

bp 

555.5 

(       90° 

0° 

[8]  C 


=  51.56  B.t.u. 


V  9.028 

If  the  apparent  displacement  in  cubic  feet  per  minute  as  deter- 
mined by  expression  [5]  be  multiplied  by  the  cooling  effect  per 
cubic  foot  as  determined  by  expression  [8],  the  result  will  be  the 
apparent  capacity  of  the  compressor  expressed  in  B.t.u.  per 
minute,  which  value  divided  by  200  gives  the  apparent  tonnage 
capacity  of  the  compressor  per  twenty-four  hours.  Expressed  as 
an  equation: 

f     D     \     f     °     \ 

I         Apparent          \     ..     I      Cooling  effect      \ 
I      displacement      j  I      in  B.  t.  u.  per      I 

V        per  min.      J  V         cu.  ft.         J 


Cooling 
effect  in 
tons  per 
24  hrs. 


/      B.  t.  u.  per  min. 
equivalent  to  one 
\        ton  per  24  hrs. 


561.15X51.56 
200 


=  144.66  tons. 


CUBIC  FEET  DISPLACEMENT  PEE  TON 
Since  200  B.t.u.  per  minute  is  the  equivalent  of  a  ton  per 

twenty-four  hours,  200  divided  by  51.56,  the  number  of  B.t.u.  of 

cooling  effect  available  per  cubic  foot  under  standard  conditions 
*  For  various  values  of  the  specific  heat  of  anhydrous  ammonia  determined 

by  a  number  of  authorities  see  Transactions  of  A.  S.  M.  E.,  pp.  522-3,  Vol. 

26,  1905. 


CAPACITY  OF  REFRIGERATING  MACHINES    133 

gives  3.88,  the  number  of  cubic  feet  of  gas  that  must  be  actually 
displaced  per  ton.  Assuming  that  the  compressor  has  a  displace- 
ment efficiency  of  80  per  cent  the  apparent  displacement  per  ton 
will  be  3.88  -.80  =  4.85  cubic  feet.* 

APPROXIMATE  NOMINAL  CAPACITY  OF  COMPRESSORS 

Dividing  the  constants  of  equations  [4]  and  [5]  by  5  (see  foot- 
note) gives  equations  [9]  and  [10],  which  will  be  found  convenient 
in  arriving  at  the  approximate  nominal  capacity  of  a  compressor 
when  its  dimensions  and  speed  of  operation  are  known. 

[9]  Tons  =  (fin  0.000181806 

[10]  Tons  =  d2  PS  0.00109081 

Substituting  values  as  above, 

=  19X19  X38  X45  X0.000181806  =  112.23  tons. 
=  19  X 19  X285  X0.00109081  =  112.23  tons. 

The  above  equations  give  approximate  results  only,  and  only 
in  the  special  case  of  standard  conditions  and  approximately  80 
per  cent  compressor  displacement  efficiency.  To  find  the  capacity 
of  a  compressor  in  the  general  case  in  which  it  is  operated  at  other 
back  and  head  pressures,  the  cooling  effect  per  cubic  foot  actual 
displacement  must  be  determined  in  each  case  by  equation  [8]. 

Furthermore,  since  the  efficiency  of  ammonia  compressors 
is  subect  to  wide  variations,  both  through  diversity  of  design  and 
diversity  of  operating  conditions  to  which  the  same  machine  is 
often  subjected,  the  efficiency  of  the  individual  compressor  should 
be  determined  under  its  own  operating  conditions.  This  can  be 
accomplished  most  accurately  by  determining  the  quantity  of 
refrigerating  fluid  actually  passing  through  the  system  and  com- 
paring this  amount  with  the  apparent  amount  computed  from  the 
displacement  of  the  compressor. 

CAPACITY  DETERMINED  BY  TEST — WEIGHING  PRIMARY  REFRIG- 
ERANT 

The  best  way  to  determine  the  amount  of  liquid  refrigerant 
is  to  weigh  it.  Fig.  41  represents  a  condenser,  a  pair  of  weighing 
tanks  and  their  connections.  For  testing,  crosses  are  inserted  in 

*  The  above  is  arrived  at  on  the  basis  of  unity  taken  as  the  latent  heat  of 
anhydrous  ammonia.  The  somewhat  higher  value  of  1.1  sometimes  employed 
would  make  the  required  actual  displacement  about  4  cubic  feet  and  the 
apparent  about  5, 


134  ELEMENTARY  MECHANICAL  REFRIGERATION 

the  inlet  and  outlet  lines,  and  valves  and  additional  pipes  are 
attached  as  indicated.  When  using  the  weighing  tanks,  the  outlet 
valve  D  is  closed  or  blanked  off  and,  as  the  valves  in  the  new  con- 
nections are  closed,  the  liquid  refrigerant  collects  in  the  receiver. 


from  Compressor 


To  Refrigerator 
Fig.    41. — Diagram   of   System   for   Weighing   Liquid   Refrigerant 

The  weighing  tank  A  is  filled  by  opening  valves  E  and  G,  after 
which  valve  G  is  closed  and  the  gross  weight  of  the  tank  and  its 
contents  is  determined.  The  weight  of  the  refrigerant  is  then 
found  by  subtracting  the  net  weight  of  the  tank  and  the  liquid  in 
the  bottom  connections.  While  the  liquid  in  tank  A  is  being 
weighed,  tank  B  is  supplying  the  cooler  through  valve  J.  Alter- 
nate filling  and  emptying  of  the  two  tanks  allows  the  operation 
of  the  plant  to  proceed  without  interruption.  When  employing 
this  method  for  weighing  the  refrigerating  liquid,  it  is  necessary 
that  the  pipes  connecting  with  the  weighing  tanks  be  sufficiently 
long  to  insure  flexibility  to  the  system.  The  liquid  level  should 
never  be  allowed  to  rise  to  the  pipes  M  and  N,  as  any  liquid  other 
than  that  vertically  over  the  drums  will  not  be  weighed  correctly. 


CAPACITY  OF  REFRIGERATING  MACHINES     135 

TONNAGE  COMPUTED  FROM  QUANTITY  OF  REFRIGERANT 

The  number  of  units  of  cooling  effect  available  in  the  evapora- 
tion of  one  pound  of  ammonia  under  standard  conditions  has  been 
found  by  equation  [7]  to  be  465.5.  The  amount  of  ammonia 
required  per  ton  is  accordingly 

200  200 

— :  =—    —  =0.42964  pounds  per  minute. 
Rbp-S^-tz)     465.5 

equivalent  to  25.778  pounds  per  hour,  or  618.7  pounds  per  twenty- 
four  hours. 

If,  for  example,  it  is  found  by  test  that  3,000  pounds  of  liquid 
ammonia  per  hour  pass  through  a  refrigerating  system,  the  com- 
pression unit  of  which  is  a  19x38-inch  double-acting  compressor 
running  at  45  revolutions  per  minute  under  standard  conditions, 
the  cooling  effect  produced  is  found  to  be 

=  116.37  ton, 

ACTUAL  DISPLACEMENT  EFFICIENCY  OF  COMPRESSOR 

Obviously,  the  efficiency  of  the  compressor  can  be  approxi- 
mated by  dividing  the  probable  cooling  effect,  as  determined  by 
calculation  based  on  the  properties  of  the  liquid,  by  the  tonnage 
computed  from  the  apparent  displacement  per  minute  in  cubic 
feet  as  calculated  from  the  dimensions  of  the  compressor.  Ex- 
pressed as  an  equation  this  becomes 

Actual 

Cooling  effect       116.37 

[11]  Actual  Efficiency  = =—     -=80.4% 

Apparent          144.66 

Cooling  effect 
APPROXIMATE  DISPLACEMENT  EFFICIENCY  OF  COMPRESSOR 

In  the  majority  of  cases  the  tonnage  capacity  of  the  system  is 
required  with  reasonably  close  accuracy,  but  it  is  often  impracti- 
cable to  weigh  the  ammonia.  In  such  cases  a  somewhat  less  accu- 
rate estimate  of  the  efficiency  of  the  compressor  can  be  made  with 
the  assistance  of  an  indicator.  For  all  practical  purposes  the 
weight -of  ammonia  gas  may  be  considered  proportional  to  its 
absolute  pressure,  and  within  narrow  limits  the  amount  of  refrig- 
eration represented  by  a  cubic  foot  of  ammonia  gas  will  likewise 
be  proportional  to  its  absolute  pressure.  From  this  it  follows  that 


136  ELEMENTARY  MECHANICAL  REFRIGERATION 


anything  tending  to  reduce  either  the  number  of  cubic  feet  of  gas 
that  a  compressor  handles  or  lower  the  pressure  at  which  it  is 
handled,  proportionately  reduces  the  capacity  of  the  compressor. 
Graphically  this  is  illustrated  and  the  actual  amount  of  the  re- 
duction in  capacity  is  determined  as  follows: 


Spring  -40  Ib. 
R.p  m.-45lb. 


A+mospheric  Line- 
Factor  of  Efficiency=86.fx88.6=76.2%> 


|<- — -4.22-100%- •- > 

j!:^K%%%£#^ 

Area  =  4.22"x0.575"=  2.426°" 


0.575x40 


-3.74  -88.6/0 


H 


A  rea  =  J.  74  x  0. 495  =>  1. 85J 


f ,h 

0  ^95^40" 
19.8  fb. 
86.1%, 

y////////////////////////////A I 

Factor  of  Efficiency  =  -fr^  =  76.2% 

Fig.  42. — Diagram  Showing  Method  of  Determining  Approximate  Com- 
pressor Efficiency  from  Indicator  Diagrams 


Having  taken  an  indicator  diagram,  such  as  that  shown  in 
Fig.  42,  draw  the  lines  a  6  and  c  d  representing,  respectively,  the 
actual  back  pressure  in  the  suction  pipe,  as  indicated  by  a  gauge, 
and  the  line  of  absolute  vacuum.  Next,  determine  /,  the  point 
at  which  the  suction  valve  first  opens  to  admit  cold  gas  to  the 
compressor  cylinder.  This  point  is  the  intersection  of  the  admis- 
sion line  e  f  and  the  re-expansion  line  forming  the  heel  of  the  dia- 
gram. Draw  a  vertical  line  /  g  through  this  point  and  other  ver- 
tical lines  e  c  and  6  d  through  the  ends  of  the  diagram.  These 
horizontal  and  vertical  lines  form  two  rectangles.  The  larger  one 
a  6  d  c  incloses  a  smaller  one  eh  d  c  which,  in  turn,  is  made  up  of 
two  still  smaller  rectangles  e  f  g  c  and  fhdg. 


CAPACITY  OF  REFRIGERATING  MACHINES    137 

In  the  case  under  consideration  the  cylinder  back-pressure  line 
a  b  scales  4.8  pounds  above  the  atmospheric  line  j  i,  making  the 
absolute  back  pressure  within  the  cylinder  approximately  19.8 
pounds.  The  observed  suction  pressure  in  the  suction  line  is  8 
pounds  gage  or  approximately  23  pounds  absolute,  of  which  the 
19.8  pounds  is  86.1  per  cent.  This  means  that  on  account  of  the 
fall  in  back  pressure,  in  passing  through  the  suction  valves  and 
ports  in  entering  the  compressor  cylinder,  each  cubic  foot  of  gas 
represents  only  86.1  per  cent  as  much  ammonia  by  weight  as  it 
would  had  no  resistance  been  encountered  and  the  cylinder  back 
pressure  been  23  pounds,  the  same  as  in  the  suction  line. 

The  diagram  shows  that  the  compressor  from  which  it  was 
taken  had  excessive  clearance.  Due  to  the  re-expansion  of  the 
high-pressure  gases  remaining  in  the  clearance  spaces,  the  opening 
of  the  suction  valve  is  delayed  until  the  piston  has  reached  point 
/  in  the  suction  stroke.  Cold  returning  ammonia  gas  can  enter  the 
compressor  cylinder  only  during  the  time  the  piston  is  passing 
from  /  to  the  end  of  its  stroke.  The  full  length  of  the  diagram 
represents  the  full  stroke  of  the  piston  and  a  displacement  of  100 
per  cent  of  the  full  volume  of  the  cylinder.  In  this  case,  however, 
11.4  per  cent  of  the  volume  is  occupied  by  re-expanding  hot  gas 
which  reduces  the  amount  of  cold  gas  that  can  enter  the  compressor 
to  88.6  per  cent.  In  other  words,  the  actual  displacement  of  the 
compressor  in  cubic  feet  is  only  88.6  per  cent  of  the  apparent 
displacement,  based  on  the  cylinder  dimensions  only. 

Now,  the  88.6  per  cent  of  the  gas  discharged  weighs  only  86.1 
per  cent  as  much  as  indicated  by  the  pressure  gauge  on  the  suction 
line,  so  that  the  number  of  pounds  of  ammonia  actually  discharged 
by  the  compressor  was  only  88.6X86.1  per  cent  of  what  would  be 
discharged  by  a  compressor  in  which  there  is  no  clearance  or  resis- 
tance offered  to  the  gas  in  passing  through  the  suction  valves. 

APPARENT  DISPLACEMENT 

Graphically,  the  length  a  b  of  the  large  rectangle  a  b  d  c  repre- 
sents the  compressor  cylinder  volume,  and  the  height  b  d  the 
absolute  suction-gas  pressure  in  the  return  line  outside  the  com- 
pressor. The  product  of  a  b  and  b  d,  or  cubic  feet  and  weight  per 
cubic  foot, — since  the  weight  of  a  gas  depends  upon  the  abso- 
lute pressure — represents  the  apparent  displacement  per  stroke 
in  pounds. 


138  ELEMENTARY  MECHANICAL  REFRIGERATION 

ACTUAL  DISPLACEMENT 

The  length  e  f  of  the  rectangle  e  f  g  c  represents  that  part 
of  the  compressor-cylinder  volume  filled  by  the  cold  gas;  and  the 
high  gf,  the  absolute  suction  pressure  within  the  cylinder.  The 
product  of  ef  and  g  f  represents  the  actual  displacement  per  stroke 
in  pounds,  or  the  apparent  displacement  minus  the  re-expanded 
hot  gas  represented  by  the  rectangle  /  h  d  g. 

APPROXIMATE  DISPLACEMENT  EFFICIENCY 

The  approximate  displacement  efficiency  of  the  compressor 
is  represented  by  the  ratio  of  the  area  of  the  small  to  the  large 
rectangle  and  will  be  found  to  be  numerically  equal  in  this  case 
to  76.2  per  cent  regardless  of  the  units  employed  in  measuring  the 
areas.  Using  inches 

3.74x0.495     1.851 


4.22X0. 
or  using  pounds  pressure  and  per  cent  stroke 

19.8X88.6 
23X100     =76.2  per  cent. 

Example: 

The  apparent  number  of  cubic  feet  of  ammonia  gas  discharged 
per  minute  by  a  19x38-inch  double-acting  compressor  running  at 
45  revolutions  per  minute  has  already  been  found  to  be  561.15. 
If  it  is  found,  by  the  indicator-diagram  method  just  described, 
that  the  displacement  efficiency  is  76.2  per  cent,  the  acutal  number 
of  cubic  feet  discharged  will  be 

0.762X561.15  =  427.59  cubic  feet 

which,  multiplied  by  the  number  of  British  thermal  units  of  refrig- 
eration represented  in  each  cubic  foot  of  ammonia  gas  actually 
displaced  gives  the  total  cooling  effect  of  the  machine  expressed 
in  British  thermal  units  per  minute.  This  quantity  divided  by 
200  reduces  the  capacity  to  tons  per  24  hours.  Under  standard 
conditions  the  number  of  British  thermal  units  per  cubic  foot  was 
found  above  to  be  51  .56,  and,  under  standard  conditions,  the  ton- 
nage capacity  of  the  compressor  under  consideration  when  oper- 
ating at  the  determined  efficiency  of  76.2  per  cent  is 


CAPACITY  OF  REFRIGERATING  MACHINES    139 

561.15X0.762X51.56 

—  —  —  —  —  =  1  10  .  23  tons  per  24  hours. 

COMPUTATION  OF  CAPACITY 

To  expedite  the  figuring  of  capacities,  not  only  under  standard 
but  also  under  other  conditions,  the  accompanying  tables  of  con- 
stants have  been  derived.  To  determine  the  tonnage  capacity  of  a 
double-acting  compressor  of  any  size  operating  at  any  piston 
speed  and  under  various  conditions  of  head  and  back  pressure  it 
is  necessary  only  to  substitute  appropriate  values  from  these 
tables  in  the  following  equations. 

Since  200  B.t.u.  per  minute  is  the  equivalent  of  one  ton  per 
24  hours,  the  tonnage  capacity  T  of  a  compressor  will  be  equal 
to  the  number  of  cubic  feet  of  gas  D  actually  displaced  per  min- 
ute multiplied  by  the  number  of  British  thermal  units  of  cooling 
effect  C  available  per  cubic  foot  of  gas  actually  displaced,  divided 
by  200.  But  the  actual  displacement  is  equal  to  the  apparent 
displacement  D  (figured  from  the  dimensions  and  speed  of  the 
machine)  multiplied  by  E,  the  displacement  efficiency  of  the  com- 
pressor, which  may  be  assumed  either  from  knowledge  of  the  de- 
sign, or  calculated  from  the  indicator  diagrams  in  accordance  with 
the  above  method,  or  determined  by  weighing  the  liquid  refrig- 
erant according  to  the  method  already  described.  Expressed  as 
an  equation,  this  becomes 

[12]  T  =  C-^ 

200 

200 
or  since  —  represents  F  the  cubic  feet  required  per  ton 


but 

... 
D      -  7^  -  =  d*X  piston  speed  X  0.00545418    [5] 


from  which  the  displacement  can  be  computed  readily  when  the 
diameter  of  the  cylinder  and  the  piston  speed  are  known.  The 
piston  speed  of  a  double-acting  compressor  of  a  given  length  of 
stroke,  when  operating  at  a  given  number  of  revolutions  per  min- 
ute, may  also  be  determined  directly  from  Table  XII. 


140   ELEMENTARY  MECHANICAL  REFRIGERATION 


TABLE   XII.— PISTON   SPEED   OF   DOUBLE- 


Length 
of 
Stroke 
in 
Inches 

REVOLUTIONS  PER 

1 

24 

26 

28 

30 

31 

32 

33 

34 

35 

36 

37 

1  

0.1666 

4 

4.33 

4.66 

5 

5.16 

5.33 

5.5 

5.66 

5.83 

6 

6.16 

2  

0.333 

8 

8.66 

9.33 

10 

10.33 

10.66 

11 

11.33 

11.66 

12 

12.33 

4  

0.666 

16 

17.33 

18.66 

20 

20.66 

21.33 

22 

22.66 

23.33 

24 

24.66 

6  

1 

24 

26 

28 

30 

31 

32 

33 

34 

35 

36 

37 

8  

1.333 

32 

34.66 

37.33 

40 

41.33 

42.66 

44 

45.33 

46.66 

48 

49.33 

9  

1.5 

36 

39 

42 

45 

46.56 

48 

49.5 

51 

52.5 

54 

55.5 

10  ... 

1.666 

40 

43.33 

46.66 

50 

51.66 

53.33 

55 

56.66 

58.33 

60 

61.66 

11  

1.833 

44 

47.66 

51.33 

55 

56.83 

58.66 

60.5 

62.33 

64.16 

66 

67.83 

12  

2 

48 

52 

56 

60 

62 

64 

66 

68 

70 

72 

74 

13 

2.166 

52 

56.33 

60.66 

65 

67.16 

69.33 

71.5 

73.66 

75.83 

78 

80.16 

14  

2.333 

56 

^60.66 

65.33 

70 

72.33 

74.66 

77 

79.33 

81.66 

84 

86.33 

15... 

2.5 

60 

65 

70 

75 

77.5 

80 

82.5 

85 

87.5 

90 

92.5 

16  

2.666 

64 

69.33 

74.66 

80 

82.66 

85.33 

88 

90.66 

93.33 

96 

98.66 

17  

2.833 

68 

73.66 

79.33 

85 

87.83 

90.66 

93.5 

96.33 

99.16 

102 

104.83 

18  

3 

72 

78 

84 

90 

93 

96 

99 

102 

105 

108 

111 

19  

3.166 

76 

82.33 

88.66 

95 

98.16 

101.33 

104.5 

107.66 

110.83 

114 

117.16 

20  

3.333 

80 

86.66 

93.33 

100 

103.33 

106.66 

110 

113.33 

116.66 

120 

123.33 

22  

3.666 

88 

95.33 

102.66 

110 

113.66 

117.33 

121 

124.66 

128.33 

132 

135.66 

24  

4 

96 

104 

112 

120 

124 

128 

132 

136 

140 

144 

148 

26  

4.333 

104 

112.66 

121.33 

130 

134.33 

138.66 

143 

147.33 

151.66 

156 

160.33 

28  

4.666 

112 

121.33 

130.66 

140 

144.66 

149.33 

154 

158.66 

163.33 

168 

172.66 

30  

5 

120 

130 

140 

150 

155 

160 

165 

170 

175 

180 

185 

32 

5.333 

128 

138.66 

149.33 

160 

165.33 

170.66 

76 

181.33 

186.66 

192 

197.33 

34  

5.666 

136 

147.33 

158.66 

170 

175.66 

181.33 

87 

192.66 

198.33 

204 

209.66 

33  

6 

144 

156 

168 

180 

186 

192 

196 

204 

210 

216 

222 

38  

6.333 

152 

164.66 

177.33 

190 

196.33 

202.66 

209 

215.33 

221.66 

228 

234.33 

40  

6.666 

160 

173.33 

186.66 

200 

206.66 

213.33 

220 

226.66 

233.33 

240 

246.66 

42  

7 

168 

182 

196 

210 

217 

224 

231 

238 

245 

252 

259 

44  

7.333 

176 

190.66 

205.33 

220 

227.33 

234.66 

242 

249.33 

256.66 

264 

271.33 

4G  

7.666 

184 

199.33 

214.66 

230 

237.66 

245.33 

253 

260.66 

268.33 

276 

283.66 

48  

8 

192 

208 

224 

240 

248 

256 

264 

272 

280 

288 

296 

50  

8.333 

200 

216.66 

233.33 

250 

258.33 

266.66 

275 

283.33 

291.66 

300 

308.33 

52... 

8.666 

208 

225.33 

242.66 

260 

268.66 

277.33 

286 

294.66 

303.33 

312 

320.66 

54  

9 

216 

234 

252 

270 

279 

288 

•297 

306 

315 

324 

333 

55  

9.333 

224 

242.66 

261.33 

280 

289.33 

298.66 

308 

317.33 

326.66 

336 

345.33 

53  

9.666 

232 

251.33 

270.66 

290 

299.66 

309.33 

319 

328.66 

338.33 

348 

357.66 

60  

10 

240 

260 

280 

300 

310 

320 

330 

340 

350 

360 

370 

62  

10.333 

248 

268.66 

289.33 

310 

320.33 

330.66 

341 

351.33 

361.66 

372 

382.33 

64.... 

10.666 

256 

277.33 

298.66 

320 

330.66 

341.33 

352 

362.66 

373.33 

384 

394.66 

66.... 

11 

264 

286 

308 

330 

341 

352 

363 

374 

385 

396 

407 

68  

11.333 

272 

294.66 

317.33 

340 

351.33 

362.66 

374 

385.33 

396.66 

408 

419.33 

70.... 

11.666 

280 

303.33 

326.66 

350 

361.66 

373.33 

385 

396.66 

408.33 

420 

431.66 

72  

12 

288 

312 

336 

360 

372 

384 

396 

408 

420 

444 

*  From  Transactions  of  the  A.  S.  M.  E. 

It  is  also  obvious  that  the  apparent  displacement  is  equal  to 
the  displacement  per  foot  of  piston  travel  multiplied  by  the  number 
of  feet  of  piston  travel  per  minute.  Table  XIII  giyes  this  displace- 
ment per  foot  of  piston  travel,  and  Table  XIV  the  number  of  cubic 
feet  of  ammonia  that  must  be  actually  displaced  per  minute  by 
the  compressor  to  produce  refrigeration  at  the  rate  of  one  ton  per 
24  hours. 

Example:     The  tonnage  capacity  of  a   19x38-inch  double- 


CAPACITY  OF  REFRIGERATING  MACHINES     141 


ACTING   COMPRESSOR   IN   FEET   PER    MINUTE 


MINUTE 


38 

39 

40 

41 

42 

43 

44 

45 

46 

47 

48 

49 

50 

6.33 

6.5 

6.66 

6.83 

7 

7.16 

7.33 

7.5 

7.66 

7.83 

8 

8.16 

8.33 

12.66 

13 

13.33 

13.66 

14 

14.33 

14.66 

15 

15.33 

15.66 

16 

16.83 

16.66 

25.33 

26 

26.66 

27.33 

28 

28.66 

29.33 

30 

30.66 

31.33 

32 

32.66 

33.33 

38 

39 

40 

41 

42 

43 

44 

45 

46 

47 

48 

49 

50 

50.66 

52 

53.33 

54.66 

56 

57.33 

58.66 

60 

61.33 

62.66 

64 

65.33 

66.66 

57 

58.5 

60 

61.5 

63 

64.5 

66 

67.5 

69 

70.5 

72 

73.5 

75 

63.33 

65 

66.66 

68.33 

70 

71.66 

73.33 

75 

76.66 

78.33 

80 

81.66 

83.33 

69.66 

71.5 

73.33 

75.16 

77 

78.83 

80.66 

82.5 

84.3 

86.16 

88 

89.83 

91.66 

76 

78 

80 

82 

84 

86 

88 

90 

92 

94 

96 

98 

100 

82.33 

84.5 

86.66 

88.83 

91 

93.16 

95.33 

97.5 

99.66 

101.83 

104 

106.16 

108.33 

88.66 

91 

93.33 

95.66 

98 

100.33 

102.66 

105 

107.33 

109.66 

112 

114.33 

116.66 

95 

97.5 

100 

102.5 

105 

107.5 

110 

112.5 

115 

117.5 

120 

122.5 

125 

101.33 

104 

106.66 

109.33 

112 

114.66 

117.33 

120 

122.66 

125.33 

128 

130.66 

133.33 

107.66 

110.5 

113.33 

116.16 

119 

121.83 

124.66 

127.5 

130.33 

133.16 

136 

138.83 

141.66 

114 

117 

120 

123 

126 

129 

132 

135 

138 

141 

144 

147 

150 

120.33 

123.5 

126.66 

129.83 

133 

136.16 

139.33 

142.5 

145.66 

148.83 

152 

155.16 

158.33 

126.66 

130 

133.33 

136.66 

140 

143.33 

146.66 

150 

153.33 

156.66 

160 

163.33 

166.66 

139.33 

143 

146.66 

150.33 

154 

157.66 

161.33 

165 

168.66 

172.33 

176 

179.66 

183.33 

152 

156 

160 

164 

168 

172 

176 

180 

184 

188 

192 

196 

200 

164.66 

169 

173.33 

177.66 

182 

186.33 

190.66 

195 

199.33 

203.66 

208 

212.33 

216.66 

177.33 

182 

186.66 

191.33 

196 

200.66 

205.33 

210 

214.66 

219.33 

224 

228.66 

233.33 

190 

195 

200 

205 

210 

215 

220 

225 

230 

235 

240 

245 

250 

202.66 

208 

213.33 

218.66 

224 

229.33 

234.66 

240 

245.33 

250.66 

256 

261.33 

266.66 

215.33 

221 

226.66 

232.33 

238 

243.66 

249.33 

255 

280.66 

266.33 

272 

277.66 

283.33 

228 

234 

240 

246 

252 

258 

264 

270 

276 

282 

288 

294 

300 

240.66 

241 

253.33 

259.66 

266 

272.33 

278.66 

285 

291.33 

297.66 

304 

310.33 

316.66 

253.33 

260 

266.66 

273.33 

280 

286.66 

293.33 

300 

306.66 

313.33 

320 

326.66 

333.33 

266 

273 

280 

287 

294 

301 

308 

315 

322 

329 

336 

343 

350 

278.66 

286 

293.33 

300.66 

308 

315.33 

322.66 

330 

337.33 

344.66 

352 

359.33 

366.66 

291.33 

299 

306.66 

314.33 

322 

329.66 

337.33 

345 

352.66 

360.33 

368 

375.66 

383.33 

304 

312 

320 

328 

336 

344 

352 

360 

368 

376 

384 

392 

400 

316.66 

325 

333.33 

341.66 

350 

358.33 

366.66 

375 

383.33 

391.66 

400 

408.33 

416.66 

329.33 

338 

346.66 

355.33 

364 

372.66 

381.33 

390 

398.66 

407.33 

416 

424.66 

433.33 

342 

351 

360 

369 

378 

388 

395 

405 

414 

423 

432 

441 

450 

354.66  364 

373.33 

382.66 

392 

401.33 

410.66 

420 

429.33 

438.66 

448 

457.33 

466.66 

367.33  !  377 

386.66 

396.33 

405 

415.66 

425.33 

435 

444.66 

454.33 

464 

473.66 

483.33 

380 

390 

400 

410 

420 

430 

440 

450 

460 

470 

480 

490 

500 

392.66 

403 

413.33 

423.68 

434 

444.33 

454.66 

465 

475.33 

485.66 

496 

506.33 

516.66 

405.33 

416 

426.66 

437.33  j  443 

458.66 

469.33 

480 

490.66 

501.33 

512 

522.66 

533.33 

418 

429 

440 

451   |  462 

473 

484 

495 

506 

517 

528 

539 

550 

430.66 

442 

453.33 

464.66  476 

487.33 

498.66 

510 

521.33 

532.66 

544 

555.33 

566.66 

443.33 

455 

466.66 

478.33  490 

501.66 

513.33 

525 

536.66 

548.33 

560 

571.66 

583.33 

456 

468 

480 

492 

504 

516 

528 

540 

552 

564 

576 

588 

600 

acting  compressor  of  76.2  per  cent  displacement  efficiency  oper- 
ating at  45  revolutions  per  minute  under  168  pounds  head  pressure 
and  16  pounds  back  pressure  is 

[14]  T 


Piston  speed! 
from  Table  I 
12=285  feet  I 


I  per  minute  J 


F 

[Apparent  displacement 

per  foot  of  piston 

travel  from  Table  13 

=  1.969  cubic  feet 


[Displacement' 
i  efficiency  of 
j    compressor 
=  0.762 


Cu.  ft.  per  min.  per  ton  per  24  hours  from  Table  XIV  =  3.85 


=  111  tons 


142  ELEMENTARY  MECHANICAL  REFRIGERATION 


TABLE   XIII.— DISPLACEMENT   D    IN    CUBIC    FEET    PER   FOOT    OF   PISTON 
TRAVEL   FOR   VARIOUS-SIZED    CYLINDERS 


CUBIC  FEET  PER  INCH  OF  PISTON  TRAVEL 


CUBIC  FEET  PER  FOOT  OF  PISTON  TRAVEL 


Is 

!•§- 

lL 

:-!§ 

to  o 

(T  2  fl 

IK 

6-g  ° 

ll 

Q* 

0  Inch 

M  Inch 

^2  Inch 

M  Inch 

|9 

0  Inch 

Y±  Inch 

%  Inch 

H  Inch 

I.. 

0.00045 

0.00071 

0.00102  1  0.00139 

1  0  .  00540 

0  .  00852 

0.01224 

0.01668 

2  

0.00182 

0.00230 

0.00284  0.00344 

2....  0.02184 

0.02766 

0.03408 

0.04128 

3.... 

0.00409 

0.00480 

0.00557  0.00639 

3  !  0  .  04908 

0.05760 

0.06684 

0.07668 

4..  . 

0.00727 

0.00821 

0.00920  0.01025 

4  0  .  08724 

0.09852 

0.11040 

0.12300 

5... 

0.01136 

0.01253 

0.01375 

0.01503 

c 

0.13632 

0.15036 

0.16500 

0.18036 

6... 

0.01636 

0.01775 

"0.01920 

0.02071 

6.  .. 

0.19636 

0.21300 

0.23040 

0.24852 

7... 

0.02227 

0.02389 

0.02557 

0.02730 

7.... 

0  .  26724 

0.28668 

0  .  30684 

0.32760 

8... 

0.02909 

0.03094 

0  .  03284 

0.03480 

8  

0.34908 

0.37128 

0.39408 

0.41760 

9... 

0.03682 

0  .  03889 

0.04102 

0.04321 

9.... 

0.44184 

0.46668 

0.49224 

0.51852 

10.... 

0.04545 

0.04775 

0.05011 

0.05252 

10.... 

0.54540 

0.57300 

0.60132 

0.53024 

11.... 

0.05500 

0.05752 

0.06011 

0.06275 

11.  . 

0.66060 

0.69024 

0.72132 

0.75300 

12  

0.06545 

0.06821 

0.07102 

0.07389 

12  

0.78540 

0.81850 

0  .  85224 

0.88668 

13.... 

0.07681 

0.07980 

0.08283 

0  .  08593 

13.... 

0.92172 

0  .  95760 

0.99396 

1.03116 

14  

0.08908 

0.09229 

0.09556 

0.09888  ; 

14  

1  .  0689 

1  .  10748 

1  .  14672 

1  .  18556 

15  

0.10226 

0.10570 

0.10920 

0.11275 

15.... 

1.2271 

1  .  26840 

1.31040 

1.35300 

16... 

0.11636 

0.12002 

0.12374 

0.12752 

16... 

1.3963 

1.44024 

1.48488 

1.53021 

17.... 

0.13135 

0.13525 

0.13919 

0.14320 

17.... 

1.5762 

1  .  62300 

1  .  67028 

1.71840 

18  

0.14726 

0.15138 

0.15556 

0.15979 

18  

1.7671 

1.81650 

1.86672 

1.91748 

19.... 

0.16408 

0.16843 

0.17283 

0.17729 

19  

1  .  9689 

2.02116 

2  .  07396 

2.12748 

20.... 

0.18181 

0.18638 

0.19101 

0.19570 

20.... 

2.1817 

2.13656 

2.29212 

2  .  34840 

21.... 

0.20044 

0.20524 

0.21010 

0.21501 

21.... 

2.4053 

2.46288 

2.52120 

2.58012 

22  

0.21998 

0.22501 

2.23010 

0.23524 

22  

2.6397 

2  .  70072 

2.76120 

2  .  82280 

23.... 

0.24044 

0.24569 

0.25100 

0.25637 

23.... 

2  .  8852 

2  .  94828 

3.01200 

3.07644 

24  

0.26180 

0.26728 

0.27282 

0.27842 

24  

3.1416 

3.20736 

3.27364 

3.34104 

25.... 

0.28407 

0.28978 

0.29555 

0.30137 

25  

3.4088 

3.47736 

3  .  54666 

3.61644 

26.... 

0.30725 

0.31319 

0.31918 

0.32523 

26... 

3  .  6870 

3  .  75828 

3.83016 

3  .  90276 

27.... 

0.33134 

0.33750 

0.34373 

0.35000 

27.... 

3  .  9760 

4  .  05000 

4.12476 

4.20000 

28  

0.35634 

0.36273 

0.36918 

0.37568 

28  

4.2760 

4.35276 

4.43016 

4.50816 

29.... 

0.  38225  j 

0.38886 

0  .  39554 

0.40227 

29.... 

4  .  5870 

4.66632 

4  .  74648 

4  .  82524 

30  

0.40906 

0.41591 

0.42281 

0.42977 

30  

4.9081 

4.99092 

5.07372 

5.15724 

COOLING  EFFECT  PRODUCED  ON  BRINE 
A  method  which  avoids  opportunity  for  error  in  determining 
the  compressor  displacement  efficiency,  but  at  the  same  time  intro- 
duces another  difficulty  in  the  form  of  Brine-tank  insulation 
losses — which  fortunately  can  usually  be  more  or  less  accurately 
determined  and .  corrected  for — is  to  check  the  apparent  perfor- 
mance of  the  compressor  by  the  actual  performance  of  the  refrig- 
erating system  as  a  whole,  as  determined  by  direct  measurement 
of  the  cooling  effect  produced  on  brine,  where  it  is  regularly  em- 
ployed in  the  plant,  or  on  brine,  water,  or  some  other  fluid  of  known 
specific  heat  where  a  secondary  medium  has  to  be  introduced  for 
the  purpose  of  test.  If,  in  the  latter  case,  the  refrigerating  effect 
cannot  be  put  to  useful  work,  it  may  be  neutralized  by  artificial 


CAPACITY  OF  REFRIGERATING  MACHINES     143 


Tempera- 
ture, 
Degrees 
Fahrenheit 


ifcl 

'  ort  « 
£     Q 


OiO 

IO  ^3 
TfO 

doo 


ll 


o'c 


CO  05 


§0 

cot^ 

"#03 


AH      Q 


1 1 

-^      ft 

•a  * 


Is 


0 

(MC5 


Oi  GO 

co  >o 
•*o 


§ 


coco 

Tjt  ^4 

OCO 


s 

rt<O5 

dec 


IN  CO 
•*t^ 

do 


"*"* 
o'co 


Is 


OCO 


IN  >O 

^co 

dco 


Ss 

•^  CO 

dco 


ss 

"#O 


coco 

^0> 


OCM     OIN 


-#->o 

0(N 


SK 


TfCO 

O  N 


IN  l-H 
T*<  IN 

ON 


o 

CO  GO 

l-H  CO 

-#co 


8S 

•*t^ 
dco 


"#<N 

o'co 


ox; 

rf*00 


So, 

I-H  CO 


s 


144  ELEMENTARY  MECHANICAL  REFRIGERATION 

heat  introduced  through  the  agency  of  a  steam  coil  or  electrical 
resistance. 

The  amount  of  cooling  that  a  given  quantity  of  brine  will  do 
depends  not  only  upon  the  number  of  degrees  rise  in  temperature, 
but  upon  the  density  and  kind  of  brine. 

The  most  important  element  in  the  selection  of  the  kind  of 
brine  to  use  is  the  temperature  to  be  produced,  which  fixes  the 
temperatures  at  which  the  brine  must  be  circulated.  Saturated 
salt  brine,  by  which  is  meant  brine  so  strong  that  it  will  dissolve 
no  more  salt,  freezes  at  about  5°  Fahrenheit  below  zero  and  would 
be  safe  for  brine-tank  temperatures  above  zero. 

The  weaker  the  brine  the  higher  the  temperature  at  which  it 
freezes,  the  limit  being  reached  when  the  amount  of  salt  is  reduced 
to  nothing,  in  which  case  the  brine  becomes  water  and  freezes  at 
32°  Fahrenheit. 

Saturated  calcium  brine  freezes  at  about  55°  Fahrenheit  below 
zero  and  according  to  its  densities  is  adapted  to  brine  temperatures 
from  40°  below  zero  up.  The  specific  heat  of  either  salt  or  calcium 
brine  upon  which  depend  their  refrigerating  capacities  per  pound 
per  degree  rise  in  temperature,  decreases  as  the  strength  increases. 

The  refrigerating  capacity  of  water  per  pound  per  degree  rise 
in  temperature  is  one  British  thermal  unit.  As  salt  or  calcium 
chloride  is  added  to  the  water  this  value  decreases  until  its  value 
at  saturation  (maximum  strength)  is  only  0.77  B.t.u.  In  the  latter 
case,  about  30  per  cent  more  brine  must  be  circulated,  to  accomplish 
a  given  amount  of  cooling  for  a  given  rise  in  brine  temperature, 
than  would  be  necessary  were  the  desired  temperatures  sufficiently 
high  to  allow  water  to  be  employed  instead  of  brine  as  the  medium 
for  conveying  heat. 

APPROXIMATE  COOLING  EFFECT  TWENTY-FIVE   HEAT  GALLONS 

PER  TON 

For  ordinary  accuracy  25  "heat  gallons"  is  considered  equiva- 
lent to  a  ton  of  cooling  effect,  a  "heat  gallon"  being  the  cooling 
effect  required  to  reduce  the  temperature  of  1  gallon  of  calcium 
chloride  brine,  of  1.2  specific  gravity,  through  a  range  of  1°  Fahren- 
heit per  minute. 

The  volume  of  brine  circulated  expressed  in  cubic  feet  per  min- 
ute can  be  calculated  from  the  dimensions  and  strokes  per  minute 
of  the  pump,  due  allowance  being  made  for  slippage,  and  this  can 


CAPACITY  OF  REFRIGERATING  MACHINES    145 


be  readily  converted  into  weight  by  multiplying  by  the  weight 
of  brine  per  cubic  foot  as  given  in  the  accompanying  tables.* 

TABLE  XV.— PROPERTIES   OF     CALCIUM  CHLORIDE   BRINE 


Salt  Required 

Freezing  Point 

4|i< 

sl 

gjg 

aL 

;§«, 

'8  g 

||| 

Lbs.  per 
Gallon 

Lbs.  per 
Cu.  Ft. 

Degrees 
F. 

Degrees 

O. 

|||S 

IJ-I 

l"« 

I|§ 

CQ 

if 

«v 

3M 

+29 

-1.6 

43 

12 

3 

1.024 

0.980 

3 

I 

+27 

-2.8 

39 

27 

6 

.041 

0.964 

5 

8^2 

+25 

-3.9 

37 

36 

9 

.058 

0.936 

7 

\y% 

11M 

+23 

-5.0 

35J^ 

40 

10 

.076 

0.911 

9 

1M 

13 

+21 

-6.1 

34 

44 

11 

.085 

0.896 

10 

2 

15 

+18 

-7.8 

30^ 

52 

13 

.103 

0.884 

12 

2J^ 

17 

+14 

-10.0 

26 

62 

15 

.121 

0.868 

14 

2]^ 

19 

+4 

-15.5 

18 

80 

20 

.159 

0.844 

18 

3 

22^ 

-1.5 

-18.2 

88 

22 

.179 

0.834 

20 

26 

-8 

-22.2 

8  2 

95 

24 

.199 

0.817 

22 

4  2 

30 

-17 

-27.2 

4 

104 

26 

.219 

0.799 

24 

4.1^ 

34 

-27 

-32.8 

1"  Vacuum 

112 

28 

1.240 

0.778 

26 

5 

37^ 

-39 

-39.4 

8"       " 

120 

34 

1.305 

32 

41 

-54 

-47.7 

15"       " 

Max.  D 

en.,  32 

1.283 



30 

TABLE  XVI.— PROPERTIES   OF  SODIUM  CHLORIDE   BRINE 


Salt  Required 

Freezing  Point 

Ilij 

|% 

il£ 

o~S 
?*£ 

ll 

III 

Lbs.  per 
Gallon 

Lbs.  per 
Cu.  Ft. 

Degrees 
F. 

Degrees 
C. 

S§£[j 

<o£* 

M  0§ 

aj« 

|1« 

Q«3 

&1I 

"o 

y 

dff 

ff 

0.084 

0.63 

+30.5 

-0.8 

45 

4 

l 

1.007 

0.992 

1 

0.169 

1.26 

+29.3 

-1.5 

43.5 

8 

2 

1.015 

0.984 

2 

0.212 

1.58 

+28.6 

-1.9 

42.5 

10 

3 

1.019 

0.980 

2.5 

0.256 

1.92 

+27.8 

-2.3 

42 

12 

3.5 

1.023 

0.976 

3 

0.300 

2.24 

+27.1 

-2.7 

41.5 

14 

4 

1.026 

0.972 

3.5 

0.344 

2.57 

+26.6 

-3.0 

40 

16 

4.5 

1.030 

0.968 

4 

0.433 

3.24 

+25.2 

-3.8 

39 

20 

5.5 

1.037 

0.960 

5 

0.523 

3.92 

+23.9 

-4.5 

37.6 

24 

6.5 

1.045 

0.946 

6 

0.617 

4.63 

+22.5 

-4.7 

35.5 

28 

7.6 

1.053 

0.932 

7 

0.708 

5.3 

+21.2 

-5.3 

34.5 

32 

8.7 

1.061 

0.919 

8 

0.802 

6.0 

+  19.9 

-6.7 

33 

36 

9.7 

1.068 

0.905 

9 

0.897 

6.7 

+  18.7 

-7.4 

31.5 

40 

10.7 

1.076 

0.892 

10 

1.092 

8.2 

+16.0 

-8.9 

29.2 

48 

12.6 

1.091 

0.874 

12 

1.389 

10.4 

+12.2 

-11.0 

25.5 

60 

15.7 

1.115 

0.855 

15 

1.928 

14.4 

+6.1 

-14.7 

20.3 

80 

20.4 

1.155 

0.829 

20 

2.376 

17.78 

+1.2 

-16.5 

16.5 

96 

24 

1.187 

0.795 

24 

2.488 

18.68 

+0.5 

-17.3 

16 

100 

25 

1.196 

0.783 

25 

2.610 

19.5 

-1.1 

-18.2 

14.8 

25.8 

1.204 

0.771 

26 

-4.7 

-20.1 

12.5 

29 

Example : — It  is  found  by  test  that  the  brine  pump  of  a  brine- 
circulating  system  discharges  1,000  gallons  of  brine  per  minute, 
the  temperature  of  the  warm  return  brine  being  7°  Fahrenheit 

*  The  specific  gravity  of  a  substance  is  the  ratio  of  the  weight  of  that  sub- 
stance to  the  weight  of  the  same  volume  of  pure  water  at  its  temperature  of 
maximum  density  at  39  degrees  Fahrenheit,  at  which  temperature  it  weighs 
62.425  pounds  per  cubic  foot.  The  weight  per  cubic  foot  of  brine  given  in 
the  table  is  determined  by  multiplying  62.425  by  the  specific  gravity  as 
determined  by  a  salinometer  or  other  similar  hydrometric  instrument. 


146   ELEMENTARY  MECHANICAL  REFRIGERATION 

higher  than  the  outgoing  cold  brine.  One  thousand  gallons  and 
7°  rise  is  equivalent  to  7,000  heat  gallons,  which,  divided  by 
25,  the  approximate  number  of  heat  gallons  per  ton,  gives  280  as 
the  approximate  tonnage  capacity  at  which  the  system  is  oper- 
ating. 

This  rule  is  intended  to  apply  roughly  to  brines  of  the  higher 
densities,  and,  since  it  does  not  take  into  consideration  possible 
variations  in  the  value  of  the  specific  heat  of  the  brine,  it  cannot  be 
expected  to  apply  accurately  to  brines  of  all  densities.  For  ex- 
ample, according  to  formula  [15]  the  amount  of  refrigeration  pro- 
duced by  the  circulation  of  200  pounds  of  water  per  minute  with 
a  rise  in  temperature  of  1°  Fahrenheit  would  be 

200X1X1 


According  to  the  rule,  which  ignores  the  specific  heat  of  water, 
which  is  unity,  the  cooling  effect  would  be,  since  200  pounds  of 
water  is  24  gallons, 

(Gals,  per  min.)  24 

=  —  =  0.96  ton 


(No.  of  heat  gals,  per  ton)     25 

ACTUAL  COOLING  EFFECT 

If  we  have  the  specific  information  that  the  brine  is  of  a  density 
of  120°  salinometer,  corresponding  to  a  specific  gravity  of  1.305, 
weighing  1.305X62.425  =  81.464  pounds  per  cubic  foot,  and  that 
the  specific  heat  of  the  brine  of  this  density  is  .767,  the  cooling 
effect  expressed  in  tons  per  24  hours  will  be  found  by  the  following 
equation. 

MR!     rr       WSfa-k)   .  ,.    , 

[15]  T  = — in  which 

W  =  Weight  of  brine  circulated  per  minute. 
S  =  Specific  heat  of  the  brine. 
(t\  —  t^  =  Range  in  temperature  cooled  through. 

200  =  Number  of  B.t.u.  per  minute  equivalent  to  a  ton  of 

refrigeration  per  24  hours. 

Since  there  are  7.48  United  States  gallons  in  a  cubic  foot,  the 
weight  of  the  brine  per  gallon  is 

1 .305  X  62.425-X  7.48  =  10.89 

pounds,  and  since  1,000  gallons  is  circulated  per  minute  the  weight 
(W)  to  be  substituted  in  the  foregoing  expression  is  10,890.    From 


CAPACITY  OF  REFRIGERATING  MACHINES    147 

the  table  we  find  that  the  specific  heat  of  brine  of  1.305  specific 
gravity  is  0.767  and  since  the  range  through  which  the  brine  is 
cooled  is  7°  Fahrenheit,  we  have 

10.890X0.767X7 
Tons  =  -      -  =292.34  tons. 


For  accurate  determinations  of  the  cooling  effect  the  density 
of  the  brine  should  be  determined  by  either  a  salinometer  or  some 
other  form  of  hydrometer  that  will  allow  either  the  percentage  of 
saturation  or  the  specific  gravity  of  the  brine  to  be  determined. 
In  taking  such  hydrometer  readings  care  should  be  taken  to  bring 
the  temperature  of  the  brine  to  that  at  which  the  instrument  is 
calibrated.  This  method  is  less  likely  to  lead  to  error  than  that  of 
applying  a  correction  factor  for  reducing  the  readings  taken  at 
other  temperatures  to  what  they  would  be  if  taken  at  the 
standard  temperature. 

For  very  accurate  determinations  the  amount  of  brine  cooled 
should  be  determined  by  weighing  and  its  specific  heat  determined 
by  some  competent  expert.  Thermometers  used  in  taking  the 
temperatures  of  the  secondary  medium  before  and  after  cooling, 
as  well  as  all  other  apparatus,  should  be  carefully  calibrated,  both 
before  and  after  the  test. 


CHAPTER  XI 
COLD  STORAGE  DUTY 

It  is  obviously  impossible  to  determine  with  any  great  degree 
of  accuracy  how  much  refrigeration  it  will  take  to  cool  a  number  of 
differently  shaped  cold  storage  boxes,  built  by  unknown  methods 
of  construction,  of  several  different  insulating  materials  of  un- 
known efficiencies  and  various  states  of  preservation,  into  which 
heat  is  admitted  through  the  opening  of  doors  and  radiated  from 
lights  and  workmen,  and  containing  unknown  quantities  of  dif- 
ferent kinds  of  products  of  varying  heat  absorbing  capacities, 
stored  for  different  lengths  of  time. 

When  the  above  list  of  unknown  quantities  can  be  sufficiently 
reduced,  however,  calculations  of  the  amount  of  cold  storage 
capacity  required  to  satisfy  a  certain  set  of  conditions  can  readily 
be  made.  Since  lights  and  workmen  must  necessarily  be  employed 
to  a  greater  or  less  extent,  and  since  no  insulation  can  entirely 
prevent  the  inflow  of  heat,  only  a  part  of  the  refrigeration  pro- 
duced by  the  refrigerating  plant  can  be  put  to  the  useful  work  of 
cooling  the  stored  products,  the  remainder  being  dissipated. 

Attempts  are  sometimes  made  to  estimate  cold  storage  duty 
by  determining  the  number  of  cubic  feet  of  space  to  be  cooled  and 
dividing  that  by  the  number  of  cubic  feet  that  a  ton  of  refrigera- 
tion is  supposed  to  cool  under  average  conditions.  While  it  may 
be  interesting  to  know  the  amount  of  space  cooled  by  a  ton  of 
refrigeration  under  more  or  less  similar  conditions,  such  compari- 
sons are  not  only  meaningless  but  are  positively  misleading,  when 
the  many  varying  conditions  of  operation  are  not  definitely  known. 
Since  such  calculations  are  at  best  inaccurate,  they  should  be 
made  only  on  the  basis  of  the  greatest  number  of  known  quanti- 
ties and  carefully  worked  out  assumptions  regarding  the  remaining 
unknown  quantities. 

These  determinations  may  be  simplified  by  the  following  brief 
method,  which,  together  with  the  accompanying  series  of  tables, 
will,  when  judiciously  applied,  be  found  accurate  enough  for  all 
ordinary  commercial  requirements. 

The  total  amount  of  heat  that  the  refrigerating  machine  must 


COLD  STORAGE  DUTY 


149 


remove  from  the  cold  storage  compartment,  is  made  up  as  fol- 
lows: 

a.  Latent  and  sometimes  specific  heat  of  the  products  stored. 

b.  Heat  evolved  by  lights. 

c.  Heat  given  off  by  workmen. 

d'.  Heat  absorbed  in  the  precipitation  and  freezing  of  moisture. 

e.  Heat  of  air  entering  through  open  doors. 

f.  Heat  entering  through  the  cold  storage  insulation. 

COOLING  THE  PRODUCT 

The  amount  of  refrigeration  required  to  cool  a  given  amount 
of  food  product  through  a  given  range  in  temperature  is  a  prac- 
tically fixed  quantity  for  a  given  product,  but  varies  widely  with 
different  products.  When  cooling  is  not  to  be  carried  below  the 
freezing  point  the  amount  of  refrigeration  required  may  be  found 
by  multiplying  the  specific  heat  of  the  product  by  the  number  of 
degrees  through  which  it  is  to  be  cooled.  If  the  product  is  also 
to  be  frozen,  this  amount  of  refrigeration  must  be  increased  by  the 
amount  of  the  latent  heat  of  fusion,  and  if  cooling  is  to  be  con- 
tinued below  the  freezing  point,  the  refrigeration  must  be  further 
increased  by  the  specific  heat  of  the  product  below  32°  multi- 
plied by  the  number  of  degrees  through  which  it  is  cooled  below 
freezing  point.  The  specific  and  latent  heat  of  a  number  of 
products  commonly  preserved  in  cold  storage  are  given  in  the 
following  table: 

TABLE   XVII— PROPERTIES   OF   FOOD   PRODUCTS 


PRODUCT 

Specific  Heat 
Above  32°F. 

Latent  Heat 
of  Freezing 

Specific  Heat 
Below  32°F. 

Beef  —  lean 

77 

102 

.41 

Beef  —  fat  

.60 

72 

.34 

Butter  . 

64 

.84 

Cream  

.68 

84 

.38 

Eggs 

76 

100 

.40 

Fish  

.82 

111 

.43 

Milk 

90 

124 

.47  - 

Mutton  

.67 

.84 

Oysters  

84 

114 

.44 

Poultry  
Pork  —  fat  . 

.80 
51 

105 
55 

.42 
.30 

EXAMPLE. — It  is  required  to  cool  10,000  pounds  of  freshly  killed  poultry 
through  68°  Fahr.  The  specific  heat  as  given  above  is  0.80.  The  number  of 
B.  t.  u.  to  be  removed  will  be  0.80X10,000X68  =  544,000.  Dividing  this 
result  by  144  (number  of  B.  t.  u.  per  pound  of  refrigeration),  the  amount  of 
cooling  duty  is  found  to  be  3,777.7  pounds.  If  the  poultry  is  frozen,  the  addi- 


150  ELEMENTARY  MECHANICAL  REFRIGERATION 


tional  refrigeration  required  will  be  10,000  X 105  =  1,050,000  B.  t.  u.  or  ( -=- 144) 
7,292  pounds,  and  if  additional  cooling  to  0°  Fahr.  is  required,  the  additional 
cold  necessary  will  be  10,000X0.42X32  =  134,000  B.  t.  u.  or  933.3  pounds. 
The  total  refrigeration  duty  required  to  cool  the  products  through  68°  Fahr., 
freeze  it  at  32°  Fahr.,  and  then  chill  it  to  0°  Fahr.,  would  be  3,777.7+7,292  + 
933.3  =  12,003  pounds  or  dividing  by  2,000  (pounds  per  ton),  6  tons. 

The  following  table  may  be  found  convenient  in  estimating 
the  amount  of  refrigeration  required  to  chill  beef,  pork,  and 
sausage  through  64°  Fahr.,  or  from  104°  Fahr.  to  40°  Fahr.: 

TABLE  XVIII— REFRIGERATION  REQUIRED  TO  COOL  MEATS 


Products  — 

Poultry 

Beef 
Fat 

Beef 
Medium 

Beef 
Lean 

Pork 
Fat 

Sausage 
(15%  Water) 

Specific  Heat  
B.t.u.  to  cool  1,000  pounds 
l°Fahr 

.80 
800 

.60 
600 

.68 
680 

.77 
770 

.51 
510 

.65 
650 

B.t.u.  to  cool  1,000  pounds 
64°Fahr                

51200 

38400 

43520 

49280 

32640 

41600 

Pounds    Refrigeration    per 
1,000  pounds  (64°Fahr.)  . 
Pounds  of  Meat  cooled  64° 
per  ton  Refrigeration  .... 
Average  wt.  Carcass  
Carcasses  cooled  per  ton    .  . 

355.55 
5,625 

266.66 

7,500 
750  Ibs. 
10 

302.22 

6,615 
750  Ibs. 

8.82 

333.66 

5,844 
750 
7.78 

226.66 

8,765 
250 
35.3 

228.88 
6,923 

It  will  be  noted  that  ten  750  pound  fat  beeves,  and  thirty-five 
250  pound  hogs  require  one  ton  of  refrigeration  for  the  cooling  of 
the  meat  alone.  In  estimating  the  cooling  capacity  of  a  medium 
for  packing  house  work,  a  ton  of  refrigeration  is  allowed  for  from 
five  to  seven  beeves  weighing  from  700  to  750  pounds,  and  for 
from  fifteen  to  twenty-four  hogs  weighing  250  pounds.  Still 
another  rough  rule  sometimes  employed  is  to  allow  a  ton  of  re- 
frigeration for  from  3  to  4,000  pounds  of  meats  cooled.  These 
larger  figures  are  intended  to  give  ample  reserve  capacity  to  pro- 
vide for  ordinary  insulation  and  other  losses  encountered  in 
packing  house  practice. 

WATER  COOLING 

Since  the  specific  heat  of  water  is  unity,  the  number  of  heat 
units  to  be  extracted  in  order  to  produce  a  given  drop  in  temper- 
ature of  a  given  quantity  of  water  is  found  by  simply  multiplying 
the  weight  in  pounds  by  the  range  cooled  through  in  degrees. 

If,  for  example,  20,000  pounds  of  water  is  to  be  cooled  one 
degree,  1,000  pounds  20  degrees,  400  pounds  50  degrees,  or  in 
fact  any  number  of  pounds  through  a  range  of  temperature  that 


COLD  STORAGE  DUTY 


151 


will  give  a  product  20,000  pound  degrees,  20,000  B.  t.  u.  will 
be  required  for  the  cooling. 

One  U.  S.  gallon  of  water  at  62°  F.  weighs  8.336  pounds.  The 
cooling  of  20,000  gallon  degrees  will  accordingly  require  8.336X 
20,000  or  166,720  B.  t.  u.  If  the  cooling  is  accomplished  in  24 
hours  the  amount  of  refrigeration  required  will  be  166,720-5-288,000 
=  .5789  tons.  If  done  in  one  hour  the  equivalent  rate  per  24 
hours  will  be  24  times  as  great  or  .5789X24  =  13.893  tons. 

Table  XIX  shows  the  amount  of  refrigeration  required  to  cool 
1,000  gallons  of  water  per  minute,  hour  and  24  hours  through 
different  ranges  of  temperature.  If  1,000  gallons  of  water  be 
cooled  50  degrees  in  one  hour,  the  equivalent  cooling  effect  per  24 
hours  will  be  ten  times  the  value  given  in  the  table  for  5  degrees, 
or  34.733  tons;  if  53  degrees,  ten  times  the  value  for  5  degrees,  or 
34.733  plus  that  given  for  3  degrees  or  2.0840,  making  36.817  tons. 

TABLE  XIX— REFRIGERATION  REQUIRED  TO  COOL  WATER  —  GALS.  —  DUTY 
IN  TONS  PER  24  HOURS 


Degrees 
Cooled 

1,000  Gals.  Cooled  per 

Degrees 
Cooled 

1,000  Gals.  Cooled  per 

Minute 

Hour 

24  Hours 

Minute 

Hour 

24  Hours 

1 

41.68 

0  .  6946 

.  02894 

21 

875.28 

14.5879 

.60778 

2 

83.36 

1.3893 

.05789 

22 

916.96 

15.2824 

.61672 

3 

125  .  04 

2  .  0840 

.08682 

23 

958.64 

15.9770 

.65564 

4 

166.72 

2.7786 

.11577 

24 

1000.32 

16.6716 

.69456 

5 

208.40 

3.4733 

.  14471 

25 

1042  .  00 

17.3664 

.72352 

6 

250.08 

4.1679 

.  17364 

26 

1083.68 

18.0612 

.75248 

7 

291.76 

4  .  8646 

.20259 

27 

1125.36 

18.7598 

.78142 

8 

333.44 

5  .  5590 

.23154 

28 

1167.04 

19.4584 

.81036 

9 

375.12 

6.2519 

.26048 

29 

1208.72 

20.1491 

.83931 

10 

416.80 

6.9466 

.28942 

30 

1250.40 

20  .  8399 

.86826 

11 

458.48 

7.6412 

.30836 

31 

1292.08 

21.5379 

.89721 

12 

500.16 

8.3358 

.34728 

32 

1333.76 

22.2360 

.92616 

13 

541.84 

9  .  0306 

.  37624 

33 

1375.44 

22  .  9289 

.95510 

14 

583  .  52 

9.7292 

.40518 

34 

1417.12 

23.6218 

.98404 

15 

625  .  20 

10.4199 

.43413 

35 

1458.80 

24.3147 

1.01298 

16 

666.88 

11.1180 

.46308 

36 

1500.48 

25.0076 

1.04192 

17 

708.56 

11.8109 

.49202 

37 

1542.16 

25.7023 

1.07086 

18 

750  .  24 

12.5038 

.52096 

38 

1583.84 

26  .  3970 

1.09980 

19 

791.92 

13.1985 

.54990 

39 

1625.52 

27.0918 

1  .  12874 

20 

833.60 

13.8933 

.  57884 

40 

1667.20 

27.7866 

1  .  15768 

WORT  COOLING 

Table  XX  shows  the  amount  of  refrigeration  expressed  in  tons 
per  24  hours  required  to  cool  100  bbls.  of  water  per  hour  and  one 
bbl.  per  minute  through  different  ranges  of  temperature.  To 
apply  this  table  to  wort  cooling  multiply  the  number  of  bbls.  of 
31  gallons  by  the  specific  gravity  of  the  wort  and  this  product  by 
the  specific  heat  of  the  wort  corresponding  to  the  specific  gravity 
as  shown  in  Fig.  43. 


152   ELEMENTARY  MECHANICAL  REFRIGERATION 


TABLE  XX— REFRIGERATION  REQUIRED  TO  COOL  WATER  (BBLS.  OF  31  GALS.) 
DUTY  IN  TONS  OF  REFRIGERATION  PER  24  HOURS 


Degrees 
Cooled 

100  Bbls.  of  31 
Gals.,  per  Hour 

1  Bbl.  of  31 
Gals.,  per  Min. 

Degrees 
Cooled 

100  Bbls.  of  31 
Gals.,  per  Hour 

1  Bbl.  of  31 
Gals.,  per  Min. 

1 

2.1545 

1  .  2927 

21 

45.2445 

27  .  1467 

2 

4.3090 

2.5854 

22 

47.3990 

28.4394 

3 

6.4635 

3.8781 

23 

49  .  5535 

29.7331 

4 

8.6180 

5  .  1708 

24 

51.6988 

31.0248 

5 

10.7725 

6.1635 

25 

53  .  8625 

32.3175 

6 

12.9270 

7.7562 

26 

56.1370 

33.6102 

7 

15.0815 

9.0489 

27 

58.1715 

34  .  9029 

8 

17.2360 

10.3416 

28 

60.3260 

36.1956 

9 

19.3905 

11.6343 

29 

62.4805 

37.4883 

10 

21.5950 

12.9270 

30 

64.6350 

38.7810 

11 

23.6995 

14.2197 

31 

66.7895 

39.0737 

12 

25  .  8494 

15.5124 

32 

68.9440 

41.3664 

13 

28.0685 

16.8051 

33 

71.0985 

42.6591 

14 

30.1630 

18.0978 

34 

73.0530 

43.9518 

15 

32.3175 

19.3905 

35 

75.4075 

45  .  2445 

16 

34.4720 

20.6832 

36 

77.5620 

46.5372 

17 

36  .  5265 

21.9759 

37 

79.7165 

47  .  8299 

18 

38.7810 

23.2686 

38 

81.8710 

44.1226 

19 

40.9355 

24.5613 

39 

83  .  9255 

50.4153 

20 

43.0900 

25.8540 

40 

86.1800 

51.6581 

TABLE  XXI— PRODUCTS  OF  SPECIFIC  GRAVITY  AND  SPECIFIC  HEAT  OF  WORT 
OF  DIFFERENT  PER  CENT  STRENGTH 


Strength    % 

Product 

Strength 

Product 

8 

0.9742 

15 

0  .  9499 

9 

0.9741 

16 

0.9463 

10 

0.9665 

17 

0.9426 

11 

0.9631 

18 

0.9390 

12 

0.9609 

19 

0  .  9353 

13 

0.9571 

20 

0  .  9320 

14 

0.9536 

Refrigeration  required  to  cool  wort  =that  required  to  cool  equal  quantity  of  water,  multi- 
plied by  the  above  "product"  corresponding  to  strength  of  wort. 


1.082 
1.080 

N 

•s 

ig  Table,  5.                         Curve  Showing  Variations  of 

1.078 
1.076 
1.074 
1.072 
*>'  1.070 
§  1.068 
£  1.066 
£  1.064 
0  1.062 
>»  1.060 
£1058 
£  1.056 
2  1.054 
O  1.052 
P  1.050 
S  1.048 

&io£ 

1.040 
1.038 
1.036 
1.034 
1.032 

JN 

" 

18                                     Specific  Heat  of  Wort  of 

X, 

^ 

\ 

Different^  Strengths  and 

\ 

s. 

.0.                Specific  Gravities. 

\ 

x 

L5H. 

v 

X 

i^V 

x- 

N 

s 

13 

x 

12 

Ss,        u 

TTSJ  o 

I 

1  1   Irs. 

0 

^•HC 

0 

5P«^ 

<« 

y 

o 

C»H 

<«T 

3 

>c 

« 

i 

OCOOC; 

-*• 

oxdo^^sooodcM^tDcooei^HocooiM^ 

Specific  Heat  of  Wort.   , 
Mg.43 


cooc'Wieoooc1^'^ 


COLD  STORAGE  DUTY  153 

Suppose  it  is  desired  to  find  the  amount  of  refrigeration  neces- 
sary to  cool  100  bbls.  of  wort  per  hour  having  a  strength  of 
12%  through  a  range  of  40°  F.  It  is  found  from  table  20, 
the  refrigeration  required  to  cool  a  like  amount  of  water  is 
86.18  tons.  Since  the  specific  gravity  of  the  wort,  as  determined 
from  Fig.  43,  is  1.049,  the  weight  of  the  wort  cooled  will  be  1.049 
times  as  great  as  for  water;  but  since  the  specific  heat  is  only 
.916  the  refrigeration  per  pound  will  be  only  .916  as  great. 
The  product  of  these  two  factors  .9609— given  for  different 
strengths  of  wort  in  Table  XXI— shows  that  the  amount  of  refrige- 
ration required  to  cool  a  given  quantity  of  wort  of  12%  strength  is 
.9609  as  great  as  for  the  same  quantity  of  water  or  in  the  above 
example  of  100  bbls.  per  hour,  .9609X86.18  or  82.80  tons. 

The  same  result  might  have  been  obtained  from  Table  XIX  by 
first  reducing  the  quantity  in  bbls.  to  gallons,  or  direct  from  the 
following  equation  in  which  for  clearness  the  above  values  have 
been  substituted. 

(Bbls.  of\    /  Gals.    \    /Wt.waterv    /    No.  de-    \    /  Specific  \     /  Specific  \ 
wort  per  \  (  per  bbl.  ]  (  per  gal.,   \  /     grees  F.     \  (    gravity    \  (   heat  of   \    /  Rate  of  \ 
hour      /  \     wort     /  V        Ibs.         /  \      cooled       I  \    of  wort    /  V      wort      /  /     cooHne      \ 
B=10Q/  \  G=31  /   \  L=8.34  /   \(tl_t2)=40/  \Sq=1.049/   \Sp=.916M    Tons    per    ) 
(B.t.u.  per  hour  equivalent  to  a  ton  of  refrigeration  per  24  hours=12000)        \      24  hrs.       / 
[16]  \T  =  82.80/ 

This  expression  when  applied  to  wort  cooling  expressed  in  bbls. 
of  31  gallons  cooled  per  hour,  becomes: 

Tons  =  .021545  X  (t  -  ti)  Xsg.  Xsh.  in  which 

(t  -  t^  =  range  of  temperature  cooled  through.     (40°  F.) 
Sg.=  specific  gravity  of  the  wort.     (1.049) 
Sh.  =  specific  heat  of  the  wort.     (.916) 

which  values  substituted  in  the  above  equation  give  tons  per  24 
•hours  =  82. 80  as  above. 

LIGHTS 

The  heat  generated  by  artificial  lights  in  cold  storage  com- 
partments often  becomes  of  considerable  importance.  The 
amount  of  refrigeration  required  to  neutralize  the  heat  radiated 
by  electric  lights  depends  on  the  candle  power  of  the  lights 
and  their  efficiency,  expressed  in  watts  per  candle  power.  If, 
for  example,  an  ordinary  low  efficiency  lamp  consuming  3.5 
watts  per  candle  power  is  employed,  the  heat  per  16  c.  p.  will  be 
16X3.5X0.05685=3.1836  B.t.u.  per  minute  or  191.0  B.t.u.  per 
hour,  which  quantities  divided  respectively  by  0.1  and  6.0,  the 
number  of  B.t.u.  per  minute  and  hour  equivalent  to  a  pound  of 


154  ELEMENTARY  MECHANICAL  REFRIGERATION 

refrigerating  duty  per  twenty-four  hours,  gives  31.83  pounds.  One 
ton  of  refrigeration  equivalent  to  2,000  pounds  of  ice  melting 
capacity  will  accordingly  be  required  for  every  sixty-three  lights. 

The  heat  generated  by  an  ordinary  gas  light  is  4,800  B.  t.  u. 
per  hour,  to  absorb  which  requires  800  pounds  of  refrigeration  per 
twenty-four  hours  (24  X  4800  -^  144  =  800) .  On  this  basis  two  and 
one-half  gas  lights  will  absorb  a  ton  of  refrigeration  per  twenty- 
four  hours  (2000 -5- 800  =  2  J£). 

Similarly  each  workman  employed  in  cold  storage  compart- 
ments radiates  about  500  B.  t.  u.  per  hour,  equivalent  to  83i 
pounds  of  refrigeration  (24X500^-144  =  83^).  On  which  basis 
a  ton  of  refrigeration  will  have  to  be  supplied  for  every  24  work- 
men per  twenty-four  hours  (2000-^83^  =  24).  In  commercial 
practice  some  authorities  allow  a  ton  of  refrigeration  for  every  30 
workmen,  presupposing  a  radiation  of  400  B.  t.  u.  per  man. 

AIR  COOLING  AND  MOISTURE  PRECIPITATION 

Before  proceeding  to  illustrate  the  method  of  calculating  the 
amount  of  refrigeration  required  to  cool  a  mixture  of  air  and  water 
vapor  it  may  be  advisable  to  define  terms. 

Air  is  a  mechanical  mixture  of  nitrogen  and  oxygen  in  the  prac- 
tically constant  proportion  of  80  parts  of  the  former  to  20  parts 
of  the  latter,  a  very  small  per  cent.,  about  3  or  4  hundredths  of 
one  per  cent,  of  which  is  replaced  by  carbon  dioxide.  Into  this 
uniform  mechanical  mixture  water  vapor  enters  in  widely  varying 
proportions.  When  the  air  contains  all  the  moisture  that  it  can 
hold  it  is  said  to  be  saturated.  The  higher  the  temperature  of 
the  air  the  more  water  vapor  it  is  capable  of  absorbing  before  be- 
coming saturated.  At  a  given  temperature  saturated  air  always 
contains  a  certain  fixed  quantity  of  water  vapor. 

It  must  be  remembered,  however,  that  the  temperature  of  the 
air  does  not  fix  the  amount  of  moisture  that  it  contains  except  in 
the  limiting  case  of  saturation.  In  the  general  case  the  air  is  not 
saturated,  and  may  contain  different  amounts  of  water  at  the 
same  temperature  as  it  varies  in  degree  of  saturation;  or  it  may 
contain  different  amounts  of  moisture  at  the  same  degree  of  satura- 
tion at  different  temperatures.  Since  the  amount  of  water  that 
it  is  possible  for  air  to  hold  in  suspension  increases  with  increasing 
temperature,  and  decreases  with  decreasing  temperature,  it  is 
evident  that  the  air  may  or  may  not  contain  less  moisture  after 


COLD  STORAGE  DUTY 


155 


5 


gS 


iOOiO 

I  I 

Ti 


<M  <M  <M  rH  rH  rH  rH 


CO  O  GO  CO  O5 
<M  O  <M  COCO  < 
CO  O  !>•  ^t1  <N  i 


<N  (N  (M  T-l  T-H  rH  rH 


1>-CO 


cO(MOOcOiO(N 

(M(N'—  li—  IrHrH 


>  t««  t^  00  C)  CO 

'  Tfi  CO  C<l  C<>  -— ' 


100  oooo 


l.b-COO 

'ooo- 


Tj<  CO  CO  <M  (M  <M  rH 


OOI^ 
OO' 


O5  C^>  rH  t— I  rH 


oooo 


OOOOOOOO 


156  ELEMENTARY  MECHANICAL  REFRIGERATION 

cooling  than  before,  according  to  whether  or  not  the  cooling  is 
carried  below  the  temperature  at  which  the  air  becomes  satu- 
rated. Table  XXII  shows  the  amount  of  vapor  in  pounds  per  thou- 
sand cubic  feet  of  air  at  different  degrees  of  saturation  at  different 
temperatures.  At  100°  Fahr.,  for  example,  1,000  cubic  feet  of 
saturated  air  will  contain  2.82  pounds  of  water  vapor,  while  at 
75°  Fahr.  the  amount  is  only  1.33  pounds,  or  less  than  one-half 
that  quantity,  and  at  15°  Fahr.  it  is  still  further  reduced  to  about 
one-tenth  of  what  it  is  at  75°  Fahr. 

In  the  general  case,  air  cooling  involves  cooling  not  only  the 
mechanical  mixture  of  oxygen  and  nitrogen,  but  a  large  quantity  of 
water  vapor  as  well.  If  the  air  contains  just  sufficient  moisture  so 
that  the  cooling  brings  it  to  the  point  of  saturation,  the  heat  that 
must  be  abstracted  from  the  water  vapor  will  be  only  that  rep- 
resented by  the  specific  heat  of  the  vapor  and  the  number  of  de- 
grees cooled  through.  If  it  is  cooled  below  the  point  of  saturation, 
as  is  usually  the  case  in  cold  storage  practice,  not  only  the  specific 
heat  of  the  vapor  but  the  latent  heat  of  that  part  of  the  vapor 
precipitated  as  well  must  be  removed.  Generally  the  process  is 
carried  still  farther  and  the  precipitated  moisture  is  chilled  to  the 
freezing  point  and  finally  frozen,  when  not  only  the  specific  heat 
of  the  liquid  but  the  latent  heat  of  fusion  is  involved.  In  case 
the  ice  is  cooled  to  a  lower  temperature  the  specific  heat  of  the 
ice  is  also  involved. 

EXAMPLE. — It  is  required  to  cool  2,000  cu.  ft.  of  air  per  minute  from  80° 
Fahr.  to  36°  Fahr.  In  the  following  calculations  it  is  assumed  that  the 
amount  of  air  to  be  cooled  is  2,000  cu.  ft.  before  it  is  cooled,  and  not,  as  it 
might  be  construed  to  mean,  2,000  cu.  ft.  of  cooled  air. 

For  the  sake  of  simplicity  the  air  is  assumed  to  be  dry. 

Dry  air  at  80°  F.  weighs  .0731  pounds  per  cu.  ft. 

2,000  cu.  ft.  would  weigh 146.2  Ibs. 

The  specific  heat  of  air  is 0.2377 

B.  t.  u.  required  to  cool  2,000  cu.  ft.  1°  F 34.75 

B.  t.  u.  required  to  cool  2,000  cu.  ft.  44°  F 1529. 

One  ton  of  refrigeration  is  sufficient  to  dispose  of  heat  at  the 
rate  of  288,000  B.  t.  u.  per  twenty-four  hours,  or  (dividing  this 
number  by  1440,  the  number  of  minutes  in  24  hours)  gives  the 
equivalent  rate  per  minute  or  200  B.  t.  u.  per  minute. 

On  this  basis,  the  cooling  of  2,000  cu.  ft.  of  air  per  minute  from 
80°  Fahr.  to  36°  Fahr.  would  require  the  expenditure  of  1529-f- 
200  =  7.64  tons  of  refrigeration. 


COLD  STORAGE  DUTY  157 

Had  the  requirements  been  for  2,000  cu.  ft.  of  cooled  air,  the 
amount  of  refrigeration  needed  would  have  been  8.36  tons,  the 
difference  being  accounted  for  by  the  difference  of  weight  per 
cu.  ft.  of  air  at  80°  Fahr.  and  36°  Fahr.,  respectively. 

COLD  LOSSES  THROUGH  COLD  STORAGE  DOORS 

There  is  no  known  means  of  accurately  determining  loss  of 
refrigeration  through  the  opening  of  cold  storage  doors.  It  is 
possible  that  it  might  be  roughly  approximated  from  formulae 
giving  the  flow  of  gases  under  slight  differences  in  pressures,  in 
which  case  some  delicate  form  of  draft  gauge  might  be  employed 
to  show  the  excess  pressure  of  the  cold  air  on  the  inside  of  the  cold 
storage  compartment  over  that  of  the  outside  air.  The  area 
through  which  the  outward  flow  due  to  the  observed  difference  of 
pressure  would  take  place  would  be  probably  about  one-half  of 
that  of  the  opening  offered  by  the  door,  because  in  a  single  opening 
the  upper. part  would  be  given  up  to  the  inward  current  of  warm 
air. 

While  it  would  be  difficult  to  estimate  the  velocity  at  which 
cold  air  rushes  out  of  a  cold  storage  compartment,  it  is  apparent 
that  it  will  increase  as  the  difference  between  the  inside  and  out- 
side temperatures,  and  with  the  increase  in  height  of  the  cold  air 
column,  both  of  these  factors  acting  to  affect  an  unbalancing  of  the 
atmospheric  pressures  and  consequently  tending  to  produce  a  flow. 

In  this  connection  it  may  be  remarked  that  the  circulation  of 
air  in  cold  storage  compartments,  as  well  as  currents  of  air  entering 
and  leaving  the  compartment,  can  be  conveniently  studied  by 
using  smoke  as  an  indicator.  It  might  be  possible  by  means  of  a 
puff  of  smoke  and  a  stop  watch,  in  the  absence  of  a  delicate  an- 
emometer, to  roughly  determine  the  velocity  of  the  air  currents. 
The  inward  current  would  have  a  maximum  velocity  at  the  top 
of  the  opening  and  the  outward  current  at  the  bottom,  while 
somewhere  near  midway  would  be  found  a  place  with  no  per- 
ceptible current.  From  this  it  follows  that  the  volume  of  air 
lost  through  the  opening  might  be  determined  by  multiplying 
one-half  the  area  of  the  opening  by  one-half  the  maximum  velocity. 
This  product  of  the  average  velocity  in  feet  per  minute  and  the 
area  of  the  current  will  be  the  number  of  cubic  feet  per  minute 
lost  through  the  opening,  and  since  4,000  cubic  feet  per  minute 
cooled  one  degree  requires  refrigeration  at  the  rate  of  one  ton  per 


158   ELEMENTARY  MECHANICAL  REFRIGERATION 

24  hours,  it  follows  that  outside  air  at  a  temperature  of  80°  Fahr., 
rushing  into  the  cold  storage  compartments  to  take  the  place  of 
cold  air  escaping  at  a  temperature  of  40°  Fahr.,  requires  an  addi- 
tional ton  of  refrigeration  for  every  100  cubic  feet  of  flow.  To 
reduce  this  excessive  loss  to  a  minimum,  vestibules  sufficiently 
large  to  permit  one  door  to  be  closed  before  the  other  is  opened 
are  often  provided  for  doors  communicating  directly  with  the 
outside.  Where  products  alone  are  to  be  passed,  rotary  doors, 
or  in  the  case  of  ice  storage  rooms  automatically  closing  swing 
doors,  may  be  employed  to  advantage. 

INSULATION  LOSSES 

Good  heat  insulators  are  simply  poor  heat  conductors  and  poor 
heat  insulators,  good  heat  conductors — this  property  of  each 
being  numerically  the  reciprocal  of  that  of  the  other.  Since  all 
heat  insulators  are  to  some  extent  heat  conductors,  the  flow  of 
heat  through  insulated  walls  cannot  be  prevented  but  only  re- 
duced in  proportion  to  the  thickness  and  efficiency  of  the  insulation 
employed.  The  amount  of  heat  that  will  pass  through  a  square 
foot  of  cold  storage  insulation  per  24  hours,  like  that  through  other 
more  or  less  imperfect  conductors,  is  practically  proportional  to 
the  difference  in  temperature  on  the  two  sides  of  the  insulation 
and  to  the  efficiency  of  the  material  not  as  a  heat  insulator  but 
as  a  heat  conductor. 

Products  cooled  to  the  temperature  of  the  cold  storage  com- 
partment, where  uniform  temperatures  are  maintained,  require 
the  expenditure  of  no  further  refrigeration.* 

The  necessity  for  operating  the  refrigerating  plant  for  the 
preservation  of  such  products  is  therefore  due  largely  to  the  en- 
trance of  heat  through  the  insulated  walls  of  the  cold  storage 
compartments  and  the  insulation  should  be  made  as  efficient  as 
economy  will  permit.  True  economy  is  found  at  the  point  where 
the  cost  of  the  refrigeration  that  would  otherwise  be  lost  is  bal- 
anced up  against  the  cost  of  the  insulation  effecting  the  saving. 
Obviously,  the  more  it  costs  to  produce  a  ton  of  refrigeration  the 
more  it  is  economy  to  spend  for  insulation  to  conserve  the  refrigera- 
tion produced. 

*  Exceptions  to  this  general  rule  are  products  which  are  fermented  while 
in  storage,  the  process  of  fermentation  giving  rise  to  the  evolving  of  a  con- 
siderable quantity  of  heat. 


COLD  STORAGE  DUTY  159 

Thermal  conductivity  varies  widely  among  various  so  called 
insulating  materials  and  even  with  the  same  material  when  vary- 
ing amounts  of  air  and  moisture  are  present.  Table  XXIII  shows 
the  rate  of  transmission  expressed  in  B.  t.  u.  per  square  foot  per 
24  hours  per  degree  difference  in  temperature  between  the  two 
sides  of  the  insulation.  These  values  represent  efficiencies  under 
best  conditions.  In  making  computations  for  determining  the 
capacity  of  refrigerating  machines  it  is  customary  among  some 
builders  to  increase  these  values  by  from  25  to  50  per  cent.,  accord- 
ing to  the  physical  condition  of  the  insulation. 

TABLE  XXIII.— HEAT  CONDUCTIVITIES,  C,  OF  COLD  STORAGE  INSULATION 

Transmission  in  B.t.u.  per  sq.  ft.  per  degree  difference  in  temperature  inside  and  out  per 
24  hours.  Compiled  largely  from  information  published  by  the  Armstrong  Cork  Co. 

Insulating  Slabs.  B.t.u. 

1"  "Pure  Cork  Sheets"  (Granulated  Cork  united  by  heat  and  pressure) 6.5 

1"  "Rock  Wool  Composition  Boards"  (Waterproofed) 7.4 

1"  Impregnated  Cork  Board  (Granulated  Cork  and  Asphaltic  binder) 8.9 

1"  Indurated  Wood  Pulp  Board 10.0 

Built-up  Insulation  (Wood  and  Air  space) 

1"  American  Spruce 16 . 80 

(%"  Dressed  and  Matched  Spruce)  (%  Sp.)  (paper,  %  Sp.)  (%  Sp.  paper,  %  Sp.) .  .  4.75 

(%  Sp.  paper,  %  Sp.)  (1"  air  space)  (%  Sp.,  paper,%  Sp.) 4.25 

6  thicknesses  \  Sp.,  3  papers,  2  air  spaces   arranged    as  above 3.45 

8           "               "        4         "      3    "       "                                "         2.70 

10           "               "        5         "      4    "       "                                "         2.70 

(8  thicknesses  being  J^  and  2  thicknesses  being  %"  thick) 

Built-up  Insulation  Wood,  Paper  and  Fill 

(%  Sp.  paper,  %  Sp.)  (%  Sp.  paper,  %  Sp.) 4 . 75 

(     "                        "      )  (4"  Mineral  Wool)  (%  Sp.  paper,  %  Sp..) 2 . 20 

(     "           "           "      )  (8"  Mill  Shavings,  Damp)  (%  Sp.  paper,  %  Sp.) 2. 10 

)  (1"     "           "         Dry     )  (        "         "            "    ) 1.35 

"      )  (8"  Granulated  Cork)                  "        "             "    ) 1 . 90 

"      )  (1"  Pure  Sheet  Cork)                    "         "             "     ) 3.10 

%  Sp.  paper)  (1"  Pure  Sheet  Cork)  (paper,  ^  Sp.) 3 . 25 

(     "        "         )  (2"           "              "    )(       "          "      ) 2.60 

"       "         )  (3"           "              "    )  (       "          "      ) 2.25 

(     "       "         )  (4"          "             "    )  (      "          "      ) 1.20 

^,?P-^Pit:?h^Sp.).:.........  ..................                             .......  4.90 

Built-up  Insulation  (Wood,  Paper,  Air  Space  and  Fill) 

(%  Sp.  paper,  %  Sp.)  (1"  Air  Space)  (%  Sp.)  (6"  Min.  Wool)  (%  Sp..  paper,  %  Sp.) .      1 .49 
(     "         "  "      )(     "         "      )(     "     )  (6"  Gran.  Cork)  (%  Sp.,  paper,  %  Sp.)     1.46 


)(     '  )(     "     )(2"PureSh.  "   )(     "  '     )     1.60 

(     "         "  "      )  (     "         "      )  (2"  Pure  Sheet  Cork)  (paper,  %  Sp.) 2. 10 

(     "         "  "      )(     "       '"      )(3"  "  "    )(     "  "      ) 1.70 

{  -    -     ••  }[  ••    "  j$     -      «  }{  ••     -  >):::::::::  ':8 

Brick  Wall  and  Sheet  Cork 

(13"  Brick  Wall)  (2"  Pure  Sheet  Cork) 2.75 

( )  (4"          "  "    ) 1.47 

Assuming,  for  example,  a  cold  storage  box  10' X 10' X 10',  the 
superficial  surface  exposed  is  600  square  feet. 

The  insulation  may  consist  of  two  courses  of  -g-"  dressed 
and  matched  spruce  with  a  course  of  paper  between,  a  l"  air  space 
and  two  more  courses  of  spruce  with  paper  between.  The  con- 


160  ELEMENTARY  MECHANICAL  REFRIGERATION 

ductivity  of  insulation  of  this  construction  is  given  in  the  table 
as  4.25  B.  t.  u.  If  the  insulation  is  found  to  be  moist,  about 
20%  may  be  added  to  the  above  value  bringing  the  heat  trans- 
mission up  to  about  5  B.  t.  u.*  The  24-hour  duty  is  now  found 
by  multiplying  600,  the  number  of  square  feet  surface,  by  5,  the 
heat  transmission  per  square  foot,  giving  3,000  the  number  of 
B.  t.  u.  per  24  hours  per  degree  difference  in  temperature.  This 
multiplied  by  the  difference  between  the  outside  and  inside  tem- 
peratures (say  90°-36°  or  54°)  gives  162,000  B.  t.  u.  as  the  total 
heat  absorbed. 

This  divided  by  144  B.  t.  u.,  the  amount  of  heat  required  to 
melt  a  pound  of  ice,  gives  1,125  pounds  or  0.5625  tons  as  the 
amount  of  refrigeration  required  per  24  hours  to  make  up  for 
insulation  losses. 

A  simple  expression  for  pounds  of  refrigeration  K  per  24 
hours,  per  square  foot  of  insulation  having  a  B.  t.  u.  conductivity 
C  per  24  hours  per  degree  difference  in  temperature  (t—  $1),  as 
given  in  Table  XXIV,  is 

[17]  K  =  C^T- 

144 

Substituting  in  this  expression  the  values  given  in  the  above 
example  gives 

*-izr- 

144 

which  result  multiplied  by  the  total  square  feet  of  surface,  600, 
gives  1,125  pounds  as  before. 

Table  XXIV  gives  similar  values  of  K  for  different  insulation 
conductivities,  ranging  from  1  to  10  B.  t.  u.  per  square  foot  and  for 
differences  in  temperature  ranging  from  40°  to  100°. 

*As  a  matter  of  fact,  five  B.  t.  u.  per  square  foot  per  degree  difference  in 
temperature  is  often  employed  where  the  exact  value  of  the  insulation  cannot 
be  determined,  as  an  approximate  factor  for  estimating  the  total  cold  storage 
duty  required  for  small  and  medium  sized  boxes  with  insulation  of  the  average 
inferior  quality  usually  employed  in  market  and  hotel  refrigerators.  The 
amount  of  refrigerating  duty  estimated  on  this  basis  should  be  ample  to  pro- 
vide not  only  for  the  insulation  losses  but  for  the  cooling  of  the  average  small 
amount  of  product  and  the  neutralizing  of  the  amount  of  heat  generated  by 
lights,  workmen  and  entering  through  the  opening  of  doors. 


COLD  STORAGE  DUTY 


161 


To  employ  this  table  in  the  above  example,  find  constant 
K=  1.875  in  the  horizontal  line  opposite  (t-ti)=54°  and  in  the 
vertical  column  under  C  =  5.  This  factor  multiplied  by  the 
surface,  600,  gives,  as  before,  1,125  pounds,  which  divided  by  2,000 
gives  0.5625  tons  of  refrigeration  as  the  required  capacity  to  make 
up  for  insulation  losses. 

TABLE  XXIV.  —  VALUES  OF  CONSTANT,  K,  Pounds  Refrigerating  Duty 
per  Square  Foot  Wall  Surface  per  24  Hours  for  Different  Insulation  Con- 
ductivities and  Differences  in  Temperature  (t  —  ti),  Inside  and  Out. 

90°  Fahr.  (0,  assumed  outside  temperature,  minus  inside  temp,  (h),  = 
(t  —  ti),  column  2. 


144 


Inside 
Temp. 
«.) 

(t—ti) 

B.t.u.  per  Sq.  Ft.  per  Degree  Difference  in  Temperature  per  24  Hours 

1 

2 

3 

4 

5 

6 

7 

8 

9 

10 

50 

48 

40 

42 

.2772 
.2916 

.5564 
.5832 

.8346 
.8749 

1.111 
1.166 

1.391 
1.458 

1.669 
1.75 

1.926 
2.041 

2.222 
2.333 

2.5 
2.635 

2.777 
2.916 

46 

44 

.3055 

.6110 

.9165 

1.222 

1.527 

1.833 

2.139 

2.444 

2.749 

3.055 

44 
42 
40 

38 

46 
48 
50 
52 

.3194 
.3333 
.3492 
.3611 

.6388 
.6667 
.6944 
.7222 

.9582 
.9999 
1.042 
1.083 

1.278 
1.333 
1.389 
1.444 

1.597 
1.667 
1.736 
1.805 

1.916 
2. 
2.083 
2.167 

2.236 
2.333 
2.432 

2.528 

2.555 
2.666 

2.777 
2.889 

2.875 
3.000 
3.125 
3.249 

3.194 
3.333 
3.471 
3.610 

36 

54 

.375 

.750 

1.125 

1.5 

1.875 

2.25 

2.625 

3.00 

3.375 

3.750 

34 
32 
30 

56 

58 
60 

.3899 
.4028 
.4166 

.7778 
.8056 
.8332 

1.167 
1.208 
1.25 

1.556 
1.611 
1.666 

1.945 
2.014 
2.083 

2.332 
2.417 
2.5 

2.729 
2.82 
2.916 

3.119 
3.222 
3.333 

3.501 
3.625 
3.749 

3.883 
4.028 
4.166 

28 

62 

.4306 

.8612 

1.292 

1.722 

2.153 

2.583 

3.014 

3.485 

3.875 

4.306 

26 
24 
22 
20 

64 
66 

68 
70 

.4444 
.4583 
.4722 
.4861 

.8888 
.9166 
Q444 
!9722 

1.333 
1.375 
1.417 
1.458 

1.778 
1.833 
1.889 
1.944 

2.222 
2.292 
2.361 
2.431 

2.666 
2.75 
2.833 
2.917 

3.001 
3.208 
3.305 
3.403 

3.555 
3.666 
3.778 
3.889 

4.000 
4.125 
4.250 
4.375 

4.444 
4.582 
4.722 
4.861 

18 

72 

5. 

1. 

1.5 

2. 

2.5 

3. 

3.5 

4. 

4.5 

5. 

16 
14 
12 
10 
8 
6 
4 
2 

74 
76 

78 
80 
82 
84 
86 
88 

.5139 

.5278 
.5417 
.5556 
.5694 
.5833 
.5972 
.6111 

.028 
.056 
.083 
.111 
.139 
.167 
.194 
.222 

1.542 
1.583 
1.625 
1.667 
1.708 
1.75 
1.792 
1.833 

2.056 
2.111 
2.167 
2.222 
2.278 
2.333 
2.389 
2.444 

2.569 
2.639 
2.708 
2.778 
2.847 
2.917 
2.986 
3.056 

3.083 
3.167 
3.25 
3.333 
3.416 
3.5 
3.583 
3.667 

3.597 
3.695 
3.792 
3.889 
3.986 
4.083 
4.180 
4.278 

4.111 
.222 
.334 
.445 
.555 
.666 
.778 
.889 

4.625 
4.750 
4  .  875 
5.000 
5.125 
5.250 
5.375 
5.500 

5.139 
5.278 
5.417 
5.555 
5.694 
5.833 
5.972 
6.111 

0 

90 

.625 

.25 

1.875 

2.5 

3.125 

3.75 

4.375 

5. 

5.625 

6.250 

—2 
—4 
—6 

—8 
—10 

92 
94 
96 
98 
100 

.6388 
.6526 
.6666 
.6805 
.6942 

.277 
.301 
.333 
.361 
1.388 

1.916 
1.958 
2.000 
2.165 
2.083 

2.553 
2.610 
2.666 
2.72 

2.778 

3.193 
3.262 
3.333 
3.470 
3.192 

3.835 
3.913 
4.000 
4.82 
4.167 

4.468 
4.565 
4.666 
4.762 
4.861 

5.110 
5.22 
5.333 
5.442 
5.555 

5.750 
5.875 
6.000 
6.125 
6.250 

6.388 
6.526 
6.666 
6.805 
6.942 

INDEX 


Absolute  zero,  8. 
Absorber,  56,  59. 
Absorbing  mediums,  heat  and  water, 

64. 

Absorption  machines,  commercial,  54. 
counter  current  effect  in,  60. 
elementary,  68. 
invention  of,  14. 
members  of,  56. 
Morris,  40. 
water,  40. 
and  compression  machines,  origin 

of,  14. 

and  compression  machines,   com- 
pared, 53,  62. 
and  compression,  use  of  NaCl  brine 

in,  40. 

of  heat  in  cold  storage,  73. 
systems,  27,  52,  53,  97. 
Actual  capacity  of  compressors,  139. 
displacement  of  compressors,  138. 
Adiabatic  compression,  64. 
Agitation  in  plate  ice  plants,  93. 
Air,  change  in  volume  and  weight  in 

cooling,  19. 

circulation  in  refrigerator,  18. 
circulation    due    to    difference    in 

head,  19. 
circulation  natural  and  forced,  19, 

20. 
circulation  in  ice  bunker  system, 

18. 

composition  of,  154. 
cooling,  22,  154,  156. 
dry,  in  bunker  systems,  20. 
expansion  of,  under  low  pressure, 

103. 

moisture  in,  156. 
pressure,  testing  with,  100. 
saturated,  154. 


Alcohol,  boiling  point  of,  6,  78. 

freezing  point  of,  6. 
Ammonia    absorption    machine,    in- 
vention of,  14. 

absorption    machine,    commercial, 
54,  56. 

absorption    machine,    elementary, 
68. 

absorption  of,  in  silver  chloride,  52. 

amount  required  per  pound  of  ice, 
25. 

amount  required  per  100  ft.  ex- 
pansion pipe,  108. 

and  sponges,  absorbing  mediums 
64. 

and  steam  condensers   74. 

properties  of,  69. 

boiling  points  of,  6,  76. 

charge  for  ice  plants,  109. 

compression  of,  adiabatic,  64. 

compressors,  capacity  of,  139. 

compressors,  displacement  of,  130. 

compressors,  efficiency  of,  86. 

compressors,  types  of,  48. 

condition  of,  116. 

condenser  and  steam  radiator  com- 
pared, 74. 

cooling  capacity  of  liquid,  25. 

cooling  of,  131. 

cubic  feet  per  unit  of  refrigeration, 
129. 

disassociation  of,  3. 

explosions  of,  105. 

freezing  point  of,  6. 

latent  heat  of  vaporization  of,  6. 

for  water  cooling,  25. 

liquid  in  compressor,  6,  11. 

path  of,  in  absorption  machine,  59. 

pounds  per  minute  per  ton,  135. 

pounds  per  unit  of  refrigeration, 
128. 

shipping  drums,  104. 


163 


164 


INDEX 


Ammonia,  specific  heat  of,  131. 

still,  59. 

temperatures  and  pressures  of,  105. 

use  of  to  expel  air,  103. 

weight  of,  per  cubic  foot,  107. 
Amount  of  charge  of  ammonia,  105, 

107. 

Analyzer,  57,  59. 

Anhydrous  ammonia.     (See  Ammo- 
nia.) 

Approximate  displacement,  138. 
Aqua  ammonia,  cooling  of,  56. 
Atoms,  motion  of,  2. 
Audiffren  refrigerating  machine,  41. 
Automatic  control  of  feeds  in  parallel, 
39. 

expansion  valve,  35. 

motor  controlling  devices,  35. 

safety  devices,  34. 

systems   of   mechanical   refrigera- 
tion, 36. 

systems,  control  of,  37. 

systems,  working  cycle  of,  37 

water  controlling  valve,  39. 


B. 

Back  pressures,    and   temperatures, 

114. 

Blast  furnace,  refrigeration  of,  8. 
Boiler  and  expansion  coils  compared, 

74. 
Boiling  liquids,  refrigeration  by,  13. 

points,  change  of,  due  to  pressure, 
78,  110,  111. 

points  of  substances,  6,  78. 
Breweries,  sanitary  requirements  in, 

14. 
Brine,  amount  of  salt  for,  109. 

calcium  chloride,  145. 

circulating  system,  23,  31. 

coils,  120. 

coils,  defrosting  of,  120. 

cooling,  142. 

cooling  systems,  elementary,  23. 

cooler,  56,  59. 

density  of,  144. 

salt  (NaCl),  145. 


Brine,  refrigerating  capacity  of,  144. 

systems,  21,  26,  30,  32,  111. 
British  thermal  unit,  4,  126. 
Bunker  floors,  insulation  of,  20. 

system.     (See  Ice  Bunker.) 
By  passes,  47. 

C. 

Calcium  chloride  brine,  145. 
Calculation  of  ammonia  charge,  107. 
Calking  of  leaks,  101. 
Can  ice  systems,  90,  95. 
Capacity,  refrigerating,  by  test,  133. 

effects  on,  127. 

of  ammonia  compressors,  128,  129. 

of  ammonia  compressors,  nominal, 
133. 

of  refrigerating  machines,  126. 

loss  of,  119. 

Carre  absorption  machine,  14,  17. 
Caustic    potash,    as    an    absorbing 

medium,  40. 
Cement,   litharge  and  glycerine  for 

pipes,  100. 

Center  freeze  system,  94. 
Charge  ammonia,  107. 

ammonia  for  compression  side,  108. 
Charging  the  system,  102. 
Chemical  reaction,  source  of  heat,  11. 
Chimney  draught,  19. 
Circulation  of  air,  bunker  systems, 
18. 

of  brine  in  gravity  brine  systems, 

21. 

Clearance  in  compressors,  49. 
Coal,  origin  of,  80. 

stored  solar  energy,  11,  80. 
Cold  air  refrigerating  machines,  67. 

air  refrigerating  machines,  cycle  of, 
67. 

and  heat,  relative  terms,  7. 

its  production,  1. 

losses    of,    through    cold    storage 
doors,  157. 

production  of,  by  boiling  liquids,  9, 
68. 

storage,  absorption  of  heat  in,  73. 

storage  duty,  148. 


INDEX 


165 


Cold  storage  products,  cooling  of,  149. 
Combined  can  and  plate  ice  plant,  95. 
Combustion,  a  source  of  heat,  11. 

engines  for  refrigerating  plants,  16. 
Commercial  refrigerating  machines. 

25,  28,  30,  44,  45,  54,  59. 
Comparisons,  62. 
Completely    automatic   refrigerating 

systems,  36. 

Complex  substances,  distillation  of,  3. 
Compression,  of  ammonia,  154. 

machine,  invention  of,  14. 

machine     and     absorption,     com- 
pared, 53,  62. 

machine,  elementary,  66. 

machine,  gas  driven,  17. 

machine,  ether,  13. 

machine,   efficiency  for  low  tem- 
peratures, 17. 

machine,  sulphur  dioxide,  41. 

system,  44. 

system,  direct  expansion,  30. 

system,  principles  employed  in,  27. 
Compressors,     actual     displacement 
efficiency  of,  135. 

capacity  of,  129. 

capacity,  computation  of,  128. 

displacement  per  foot  piston  travel, 
142. 

double  acting,  48. 

enclosed  crank  case,  type,  51. 

efficiency  of,  86. 

liquid  ammonia  in,  116. 

lubricating  system  of,  47. 

nominal  capacities  of,  133. 

oils  for,  122. 

types  of,  47. 

temperature  regulation  of,  47. 
Compression,  wet  and  dry,  116. 
Condensation  of  steam  and  ammonia, 
74. 

vaporized  refrigerant,  25. 
Condenser  coils,  incrustation  of,  125. 

pressures   and   temperatures,  114, 

115. 
Condensers,  58,  59. 

counter  current,  46. 
Condensable  gases,  22. 


Conduction,  7. 

Conductivity  of  insulation,  159. 
Congealing  tanks,  33. 
tanks,  capacity  of,  33. 
tank  systems,  32. 
tank  systems,  losses  in,  34. 
Connections  for  charging  system,  104. 
Constant  pressure,  evaporation  at,  4. 
Contents,  table  of,  vii. 
Control  of  parallel   ammonia  feeds, 

39. 

Convection  of  heat,  7. 
Cooling  and  heating,  relative  terms, 

27 

Cooling  air,  156. 
ammonia,  154. 
brine,  142. 

cold  storage  products,  149. 
meats,  150. 

refrigerant,  29,  46,  131. 
water,  150. 
wort,  150. 
capacity  of  ice,  18. 
capacity  of  congealing  tanks,  33. 
capacity  of  liquid  ammonia,  25. 
mediums,  natural,  26,  70. 
water,  path  of,  in  absorption  sys- 
tem, 59,  60. 
Counter  current,  effect  in  absorption 

machine,  60. 
condenser,  46. 

Cycle   working   of   compression,   re- 
frigerating system,  28,  44. 
of  Audiffren  machine,  41. 
of    absorption    refrigerating    ma- 
chine, 59. 

of  cold  air  machine,  67. 
of  Morris  machine,  41. 
of  automatic  parallel  feed  system, 

39. 

of  thermostatically  controlled  sys- 
tem, 37,  38. 
Cylinder  cooling  by  direct  expansion, 

47. 
Cubical  contents  of  cylinders,  pipes, 

107. 

displacement    of    ammonia    com- 
pressors, 130. 


166 


INDEX 


D. 

Damp-proofing,  compared  to  insula- 
tion, 76. 

Davie's  experiment,  110. 
Defrosting  brine  coils,  120. 

direct  expansion  coils,  121. 
Density  of  brine,  144. 
Deodorizers,  98. 

Development  of  mechanical  refrigera- 
tion, 11. 
Direct  expansion  coils,  121. 

expansion  coils,  defrosting  of,  121. 
expansion  compression  system,  30. 
expansion  absorption  system,  22. 
expansion  surface,  heat  transmis- 
sion through,  120. 
Displacement  of  compressors,  actual, 

138. 

of  compressors,  approximate,  137. 
of    compressors,    per   foot    piston 

travel,  142. 
efficiencies    of    compressors,    129, 

135. 

efficiencies  of  compressors,  by  in- 
dicator cards,  136. 
efficiencies,  factors  of,  136. 
efficiencies,   losses  in,   due  to  re- 
expansion,  136. 
per  ton  refrigeration,  132. 
Distillation  of  complex  substances,  3. 
Distilling  apparatus,  90. 
systems,  90,  96. 
systems,  high  pressure,  90. 
Double  acting  compressors,  48,  50. 
packing  of,  50. 
piston  speeds  of,  140. 
Duty,  refrigerating,  measurement  of, 
126. 

E. 

Early  experimenters,  13. 

Economy,    relative,  of    compression 

and  absorption  machines,  17. 
Effect  of  working  pressures,  131. 
Efficiencies  of  ammonia  compressors, 

86,  135. 
Efficiency  and  pressure,  112. 


Efficiency  determined  from  indicator 

cards,  136. 

displacement  of  compressors,  129. 
loss  of,  due  to  incrustation,  125. 
Elementary  absorption  machine,  52, 

68. 

brine  system,  23,  26. 
compression  machine,  66. 
direct  expansion  system,  22. 
intermittent   absorption   machine, 

53. 

ice  making  system,  24. 
mechanical    refrigerating    system, 

22. 

Electrically  driven  plants,  34. 
Electric  lights  in  refrigerators,   153, 

154. 

welding,  102. 
Enclosed  crank  case  compressors,  51. 

lubrication  of,  54. 
Energy,  heat  a  form  of,  2. 
solar,  stored  in  coal,  80. 
Equalizer  line,  46. 

Ether  compression  machine,   inven- 
tion of,  13. 
boiling  point  of,  78. 
Exchanger,  56,  59. 
Expansion  coils,  28. 

coils,    compared   to   steam  boiler, 

74. 

coils,  ice  on,  119. 
coils,  oil  in,  122. 
coils,  surface  required,  108. 
of  refrigerant,  46. 
of  refrigerant,  behind  a  piston,  65. 
side,  compression  system,  44. 
surface,   relation  to   temperature, 

111. 

valves,  46. 

valves,  automatic,  35. 
valves,  control,  cycle  of  operations 

of,  38. 

Explosions,  ammonia,  103,  105. 
Extraction  of  heat  from  vaporized 

refrigerant,  29. 

Evaporating  temperatures,  78. 
Evaporation  at  constant  pressure,  4, 
at  fixed  temperature,  4. 


INDEX 


167 


Evaporation  of  ammonia,  pipe  sur- 
face required  for,  79. 
of  moisture  by  solar  heat,  80. 
of  liquid  refrigerant,  22. 
rate  of,  79. 
refrigeration  by,  9. 
Evaporators,    in    vacuum    distilling 
apparatus,  95,  96. 

F. 

Factor    of    displacement    efficiency, 

136. 

Faraday's  experiments,  14,  52. 
Filters,  98. 
Fittings,  100. 
Flange  joints,  100. 
Flow  of  heat,  6,  7,  76,  80. 

of  heat  compared  to  that  of  elec- 
tricity, 7. 
of  heat  compared  to  that  of  water, 

76. 

Food  products,  properties  of,  149. 
Forced  air  circulation,  20. 
Fore  cooler,  98. 
Freezing  back,  115. 
time  for  ice,  92. 
point  of  alcohol,  6. 
of  iron,  9. 
of  mercury,  9. 
of  water,  6. 

of  various  substances,  6. 
Frigorinc  mixtures,  12,  21. 
Fusion  by  application  of  heat,  2. 
Frost,  formation  of,  117. 
Frost  line,  117. 
Frosting  of  pipes,  43. 
Fusion,  latent  heat  of,  13. 

G. 

Gases,  permanent  removal  of,  123. 
cooling  capacity  of,  in  change  of 
temperature,  67. 

Gas  engine  driven  compression  ma- 
chines, 17. 

Gasification  by  absorption  of  heat,  3. 

Gasket  joints,  100. 

Gas  lights  in  refrigerators,  4,  153. 


Generators,  57,  59. 
Glycerine  and  litharge  cement,  100. 
Generation  of  heat,  5,  76. 
Gravity  brine  system,  21. 


H. 


Harrison,  work  on  compression  ma- 
chine, 14. 

Head  pressure  and  condenser  pres- 
sures, 115. 

Heat    absorbing    capacity    of    sub- 
stances, 6,  12. 

absorption  in  cold  storage,  73. 

a  form  of  energy,  2. 

and  cold,  relative  terms,  71. 

extraction  of,  from  vaporized  re- 
frigerant, 29. 

flow  of,  1,  6,  76. 

flow  of,  compared  to  that  of  water, 
7. 

flow  of,  76. 

flow  of,  due  to  difference  in  tem- 
perature, 7,  76. 

fusion  by,  3. 

gallon,  144. 

gasification  by,  3. 

gravitation  of,  75 

latent,  3. 

leak  of,  through  insulation,  76,  159. 

mechanical  equivalent  of,  5. 

passage    of    by    conduction,    con- 
vection and  radiation,  7. 

pump  compared  to  water  pump, 
62,  75. 

raising  of,  from  low  to  higher  level, 
82. 

sources  of,  11. 

specific,  3,  13. 

transmission     through     expansion 

surfaces,  120. 
Heating    and    refrigerating    systems 

compared,  72. 
Heating   and   refrigerating,   relative 

terms,  69. 
Heat  units,  derived,  4. 

negative    equivalent   to  ton    of 
refrigeration,  5. 


168 


INDEX 


High  pressure  distilling  system,  90. 

Horizontal  double  acting  compress- 
ors, 50. 

Horse  power  per  ton  of  refrigeration, 
86,  87. 

Household  type  of  refrigerating  ma- 
chine, 40,  41. 

Hydrometry,  147. 


I. 


Ice  bunker  systems,  18,  20. 

bunker   systems,    precipitation   of 
moisture  in,  20. 

bunker  systems,  temperatures  pro- 
duced in,  20. 

cooling  by,  18. 

early  production  of,  14. 

loss  of  efficiency  due  to,  in  expan- 
sion coils,  119. 

frozen    per    pound    of    ammonia 
evaporated,  25. 

freezing  systems,  laboratory  meth- 
od, 24. 

from  polluted  waters,  14. 

impurities  in,  93. 

latent  heat  of,  5. 

making  by  can  system,  90. 

making  by  center  freeze  system,  94. 

making   plants,    ammonia   charge 
for,  109. 

on  expansion  coils,  119. 

plate,  size  of,  93. 

plate  system,  operation  of,  93. 

specific  heat  of,  5. 

systems,  can  and  plate,  95. 

time  required  for  freezing  of,  92,  94. 
Impurities  in  ice,  93. 
Incrustation,  12. 

Indicator  cards,  for  determining  effi- 
ciency, 136. 
Installation  of  refrigerating  machines, 

100. 

Insulation,  compared  to  dampproof- 
ing,  76. 

economy  in,  158. 

heat  conductivity  of,  60,  76,  158, 
159. 


Insulation  of  bunker  floors,  20. 
of  condenser  coils  by  incrustation, 

125. 

Intermittent  absorption  system,  53. 
Internal  work  of  melting  and  evap- 
orating, 4. 
Iron,  fusion  point  of,  9. 

J. 

Joints,  flange,  100. 

gasket,  100. 
Joules'  experiments,  4. 

K. 

Kelvin's  experiment,  110. 
Kinetic  theory,  2. 

L. 

Laboratory  direct  expansion  system, 

22. 

brine  system,  23. 
ice  freezing  system,  24. 
Latent  heat,  3. 

use  of  in  refrigerating  processes, 

68. 

of  ice,  5,  6. 
of  fusion  and  vaporization,  3,  5, 

13. 

Leaks,  effect  of,  85. 
location  of,  101. 

Litharge  and  glycerine  cement,  100. 
Lights  in  cold  storage,  153. 
Liquefaction  of  gases  by  Faraday,  14. 
Liquid  ammonia,  cooling  capacity  of, 

25. 

in  compressor,  116. 
water  cooling  by,  25. 
Liquid  refrigerant,  evaporation  of,  9, 

22. 

system  for  weighing,  134. 
Losses,  insulation,  cold  storage  doors, 

157. 

of  efficiency  in  brine  systems,  32. 
of    efficiency    in    congealing    tank 
systems,  34. 


INDEX 


169 


Losses   through   insulation,    compu- 
tation of,  60,  159. 

Low  efficiency  due  to  low  tempera- 
tures, 86. 

temperatures,    laboratory  method 
of  production,  12. 

Lubrication  of  compressors,  47,  52. 

M. 

Matter,  change  of  state  of,  3. 

states  of,  2. 
Meats,  cooling  of,  150. 

refrigeration  required  to  cool,  150. 
Mechanical  equivalent  of  heat,  5. 
refrigeration,       development      of, 

11. 

systems  of  refrigeration,  element- 
ary, 22. 

Mediums,  refrigerating,  29. 
Melting  of  solids,  a  method   of  re- 
frigeration, 8. 

points  of  various  substances,  6. 
Mercury,  freezing  point  of,  9. 
Mixtures,  frigorific,  12,  21. 
Moisture,    precipitation    of    in    ice 

bunker  system,  20. 
precipitation   of   by   refrigeration, 

154. 

Molecular  theory,  2. 
Molecules,  effect  of  heat  on,  2. 
Morris  absorption  machine,  40. 
system,  working  cycle  of,  41. 
Motor  controlling  devices,  37. 

controlling      devices,      automatic, 

35. 

Multiple    effect    refrigerating    ma- 
chines, 89. 

N. 

Natural  circulation  of  air,  19. 
cooling  mediums,  26,  70. 
processes  of  heating  and  refrigera- 
tion, 8. 

processes  of  refrigeration  by  evap- 
oration, 9. 
Nessler's  solution,  use  of,  101. 


O. 

Ohm's  law,  7. 

Oils  for  ammonia  compressors,  122. 

Oil,  in  expansion  coils,  removal  of, 

122. 

in  refrigerating  system,  121. 
Operation  of  plate  ice  system,  93. 
of   refrigerating   machines,    steam 

driven,  16. 

of  refrigerating  machines,  gas  en- 
gine, 17. 
of  refrigerating  machines,  general, 

100. 

of  small  refrigerating  system,  43. 
Overcharge,  detection  of,  106. 
Oxy-acetyline,  102. 


P. 

Packing  of  double  acting  compres- 
sors, 30. 

Parallel  feed,  automatic  control  of, 

39. 

feed,  control,  cycle  of  operation  of, 
39. 

Perkin's  work,  13,  17. 

Permanent  gases,  removal  of,  123. 

Pipes,  cubical  contents  of,  107. 

Pipe  surface  required  for  evaporation 
of  ammonia,  79. 

Piping,  100. 

Piston  rod,  lubrication  of,  51. 

Piston  speeds,    double   acting   com- 
pressors, 140,  141. 

Pistons,  Linde  type,  50. 

Piston  travel,  displacement  per  foot 
of,  142. 

Plate  ice  s}'-stems,  agitation  in,  93. 

Plate  ice,  time  to  freeze,  92,  94. 

Plate  system,  92. 

Potassium    hydrate,     an    absorbing 
medium,  40. 

Pounds  of  ammonia,  per  pound  re- 
frigeration, 128,  143. 
of  refrigeration,  126,  128. 

Precipitation  of  moisture,  154. 
of  moisture  in  ice  bunker,  20. 

Pressures  and  efficiency,  112. 


170 


INDEX 


Pressure,  effect  of,  127. 

effect  of,  on  boiling  point,  78,  110, 

111. 

working,  effect  of,  130. 
Pressure  tanks,  45. 
Pressures  and  temperatures  of  am- 
monia, 105. 

Primary  refrigerant,  method  of  weigh- 
ing, 133. 
Production  of  dry  air  in  ice  bunker 

systems,  20. 

Properties  of  food  products,  149. 
of  matter,  2. 

of  refrigerating  mediums,  113. 
of  water  and  ammonia,  69. 
Pumps  for  heat  and  water,  62. 
Pumping  vacuum,  103. 
Purging  the  system,  124 
Pump  out  lines,  47. 


R. 


Radiation  of  heat,  7. 
Raising  of  heat,  82. 

water,  82. 
Receiver,  46. 
Rectifier,  58,  59. 
Re-expansion,  loss  of  efficiency  from, 

136. 

Refrigerant  compared  to  sponge,  26. 
Refrigerant,  condensation  of  vapor- 
ized, 25. 

cooling  of,  29,  46,  131. 

evaporation  of,  22. 

liquid,  weighing  of,  133,  134. 

selection  of,  10. 

water  as  a,  10. 

Refrigerating  at   different   tempera- 
tures, 87. 

capacity,  loss  of,  due  to  ice,  119 

capacity  of  brines,  144. 

effect,  calculation  of,  131. 

machine,  as  a  heat  pump,  75. 

machine,  capacity  of,  125. 

machine,  installation  of,  100. 

machine,  multiple  effect,  89. 

machine,  operation  of,  100. 

machine,  small  capacity,  40. 


Refrigerating    mediums,     properties 
of,  113. 

medium,  water  as,  71,  72. 

system,  charging  of,  102. 

system,  compared  to  heating  sys- 
tem, 72. 

system,  oil  in,  121. 

system,  purging  of,  123. 

system,  selection  of,  42. 

system,  testing  of,  133. 

temperatures  and  pressures,  9. 
Refrigeration,  ammonia  required  per 
ton  of,  135. 

available  in  expansion,  45. 

by  change  of  temperature  of  gases, 
67. 

by  evaporation  of  liquids,  9,  68. 

by  melting  of  solids,  8. 

by  specific  heat  of  gas,  67. 

defined,  1. 

mechanical,  11. 

necessary  to  cool  water,  150. 

necessary  to  cool  wort,  151. 

of  blast  furnace,  8. 

pound  of,  128. 

tonnage,  basis  of,  51,  127. 
Refrigerator  coils,  defrosting  of,  119. 

lights  in,  effect  of,  153. 
Regulation  of  compressor  tempera- 
tures, 47. 
Relative    temperatures    of    cooling 

water  and  refrigerants,  27. 
Repairs,  leaks,  101. 
Rusting,  leaks,  101. 


Safety  devices,  automatic,  34. 

head,  49. 
Salt,  amount  of,  for  brine,  109. 

brine,  145. 

use  of,  in  gravity  brine  systems,  21. 
Sanitary  conditions  in  gravity  brine 

system,  21. 

Saturated  air,  cooling  of,  156. 
Saturation  of  air,  154. 

of  air,  relation  to  temperature,  156. 
Scale  on  condenser  coils,  125. 

trap,  45. 


INDEX 


171 


Selection  of  refrigerating  system,  42. 
Semi-automatic  system,  35. 
Shipping  drums  for  ammonia,  104. 
Silver   chloride,    absorption   of   am- 
monia in,  52. 
Simple  comparisons,  62. 
Single  acting  compressors,  48. 
Small  machine  brine  system,  15. 
Small  machines,  types  of,  15. 
Small  refrigerating  machines,  opera- 
tion of,  43. 

Sodium  chloride  brine,  45. 
Solar  energy,  available  in  coal,  80. 
Solar  heat,  evaporation  of  moisture 
by,  80. 

heat  stored  in  coal,  11. 

radiation  source  of  heat,  11. 
Soldering  leaks,  102. 

solutions  for  pipes,  102. 
Solids,  refrigeration  by   the  melting 

of,  8. 
Solution,  effect  of,  6. 

freezing  point  of,  6. 
Sources  of  heat,  11. 
Specific  gravity  of  wort,  152. 

heat,  3. 

heat  involved  in  refrigerating  pro- 
cesses, 67. 

heat  of  ammonia,  132. 

heat  of  ice,  5. 

heat  of  steam,  constant  pressure 
and  volume,  5. 

heat  of  wort,  152. 

heat  of  solids,  liquids  and  gases,  12. 

heat,   variation  of,   with  density, 

144. 

Splash  lubrication,  52. 
Standard  conditions  of  tests,  127. 

tonnage  basis  of  refrigeration,  5. 
Static  head  and  thermal  head,  80. 
Steam  and   ammonia,   condensation 
of,  74. 

power  due  to  solar  heat,  81. 

radiator  and  ammonia  condenser 
compared,  74. 

specific  heat  of,  5. 

use  of,  for  refrigeration,  16. 
Stills,  ammonia,  59. 


Storage  tanks,  46. 

Strong  aqua,  cooling  of,  56. 

liquor,  path  of  in  absorption  sys- 
tem, 59. 

Stuffing  box,  50. 
Substances,  boiling  points  of,  6. 
heat  absorbing  capacities  of,  6,  12. 
melting  points  of,  6. 
Sulphur    dioxide    compression    ma- 
chine, 41. 

sticks,  testing  with,  101. 
Suction  lines,  insulation  of,  118. 
valves,  operation  of,  in  compress- 
ors, 49. 

System  for  weighing  liquid  refriger- 
ant, 134. 

Systems  of  refrigeration,  17,  18. 
water  and  ammonia,  compared,  69. 

T. 

Table  of  contents,  vii. 
Tanks,  congealing,  33. 
Tank  pressure,  45. 
Temperature  difference   in  brine  sys- 
tem, 111. 

difference  in  direct  expansion  sys- 
tem, 111. 

difference  of  effecting  rate  of  evap- 
oration, 79. 

Temperatures  and  corresponding  back 
pressures,  114. 

and  relation  to  expansion  surface, 
111. 

and  pressures,  ammonia,  105. 

of  saturated  air,  154. 

of  refrigerating,  9. 
Test,  standard  conditions,  127. 
Testing,  100. 

of  refrigerating  systems,  133. 

sulphur  sticks  for,  101. 

Nessler's  solution  for,  101. 
Thermal  and  static  head,  76,  80. 

conductivity,  159. 
Thermostatic  control,  36. 

control,  cycle  of  operation  of,  37. 
Thermostats,  37. 
Tonnage  basis  of  refrigeration,  5. 


172 


INDEX 


Ton  of  refrigeration,   ammonia  for, 

135,  143. 
of  refrigeration,  horse  power  for, 

86. 

unit  of  refrigeration,  127. 
Twining,  work  of,  14. 
Types  of  small  machines,  15. 


U. 

Units,  126. 

Use  of  compression  and  absorption 
machines,  17. 

V. 

Vacuum  distilling  apparatus,  95,  96. 
Vacuum,  effect  of,  on  boiling  points, 

13. 

Valves,  automatic  expansion,  35. 
suction,  operation  of,  49. 
water,  automatic,  39. 
Vaporization,  latent  heat  of,  13. 
latent  heat  of,  for  water,  5. 
temperature,   change  of,  by  pres- 
sure, 13. 
Vaporized  refrigerant,    condensation 

of,  2. 
Vertical   single    acting    compressors, 

48,  49. 

Variation  of  specific  heat  with  den- 
sity, 144. 

Volume  of  pipes,  107. 
of  air,  change  of,  in  refrigeration, 
19. 

W. 

Water  absorption  machine,  40. 
a  natural  cooling  medium,  26. 
and  ammonia,  properties  of,  69. 
and  ammonia  systems,  compared, 
69. 


Water  and  heat  pumps,  62. 

as  a  refrigerating  medium,  10,  40, 
71,  72. 

boiling  point  of,  6. 

cooling  by  liquid  ammonia,  25. 

filter,  98. 

freezing  point  of,  6. 

latent  heat  of  fusion  of,  6. 

latent  heat  of  vaporization  of,  5. 

power  and  steam  power  due  to  solar 
heat,  81. 

proofing  compared   to   insulation, 
76. 

rate  of  flow  of,  due  to  difference  in 
level,  76. 

refrigeration  required  to  cool,  150. 

ultimate  cooling  medium,  71. 

valve,  automatic,  39. 

vapors  in  air,  154. 
Weak  liquor  cooler,  56,  59. 

liquor,  path  of,  in  absorption  sys- 
tem, 59. 

Weighing,  liquid  refrigerant,  133,  134. 
Weight  of  air,  change  of,  in  refrigera- 
tion, 19. 

of  ammonia  per  cubic  foot,  107. 
Welding,  electric,  102. 
Wet  and  dry  compression,  116. 
Working  cycles,  28. 

cycles  of  automatic  systems,  37. 

limits,  85. 

mediums,  29. 

pressures,  110,  131. 
Work,  internal,  4. 

Wort,  refrigeration  required  to  cool, 
151. 

specific  gravity  of,  152 

specific  heat  of,  152. 


Z. 


Zero,  absolute,  8. 


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